Fix builders ABI backward compatibility broken in v1.33.0

* fix channel builders ABI backward compatibility broken in v1.33.0
* fix server builders ABI backward compatibility broken in v1.33.0
* makes ForwardingServerBuilder package-private

api/src/main/java/io/grpc/ForwardingServerBuilder.java

@@ -30,8 +30,7 @@
  * @since 1.33.0
  */
 @ExperimentalApi("https://github.com/grpc/grpc-java/issues/7393")
-public abstract class ForwardingServerBuilder<T extends ForwardingServerBuilder<T>>
-    extends ServerBuilder<T> {
+abstract class ForwardingServerBuilder<T extends ServerBuilder<T>> extends ServerBuilder<T> {
 
   /** The default constructor. */
   protected ForwardingServerBuilder() {}

core/src/main/java/io/grpc/inprocess/InProcessChannelBuilder.java

@@ -21,9 +21,9 @@
 
 import io.grpc.ChannelLogger;
 import io.grpc.ExperimentalApi;
-import io.grpc.ForwardingChannelBuilder;
 import io.grpc.Internal;
 import io.grpc.ManagedChannelBuilder;
+import io.grpc.internal.AbstractManagedChannelImplBuilder;
 import io.grpc.internal.ClientTransportFactory;
 import io.grpc.internal.ConnectionClientTransport;
 import io.grpc.internal.GrpcUtil;
@@ -45,7 +45,7 @@
  */
 @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1783")
 public final class InProcessChannelBuilder extends
-    ForwardingChannelBuilder<InProcessChannelBuilder> {
+    AbstractManagedChannelImplBuilder<InProcessChannelBuilder> {
   /**
    * Create a channel builder that will connect to the server with the given name.
    *

core/src/main/java/io/grpc/inprocess/InProcessServerBuilder.java

@@ -21,10 +21,10 @@
 import com.google.common.base.Preconditions;
 import io.grpc.Deadline;
 import io.grpc.ExperimentalApi;
-import io.grpc.ForwardingServerBuilder;
 import io.grpc.Internal;
 import io.grpc.ServerBuilder;
 import io.grpc.ServerStreamTracer;
+import io.grpc.internal.AbstractServerImplBuilder;
 import io.grpc.internal.FixedObjectPool;
 import io.grpc.internal.GrpcUtil;
 import io.grpc.internal.InternalServer;
@@ -72,7 +72,8 @@
  * </pre>
  */
 @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1783")
-public final class InProcessServerBuilder extends ForwardingServerBuilder<InProcessServerBuilder> {
+public final class InProcessServerBuilder extends
+    AbstractServerImplBuilder<InProcessServerBuilder> {
   /**
    * Create a server builder that will bind with the given name.
    *

core/src/main/java/io/grpc/internal/AbstractManagedChannelImplBuilder.java

@@ -0,0 +1,277 @@
+/*
+ * Copyright 2020 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.internal;
+
+import com.google.common.base.MoreObjects;
+import io.grpc.BinaryLog;
+import io.grpc.ClientInterceptor;
+import io.grpc.CompressorRegistry;
+import io.grpc.DecompressorRegistry;
+import io.grpc.ManagedChannel;
+import io.grpc.ManagedChannelBuilder;
+import io.grpc.NameResolver;
+import io.grpc.ProxyDetector;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.Executor;
+import java.util.concurrent.TimeUnit;
+import javax.annotation.Nullable;
+
+/**
+ * Temporarily duplicates {@link io.grpc.ForwardingChannelBuilder} to fix ABI backward
+ * compatibility.
+ *
+ * @param <T> The concrete type of this builder.
+ * @see <a href="https://github.com/grpc/grpc-java/issues/7211">grpc/grpc-java#7211</a>
+ */
+public abstract class AbstractManagedChannelImplBuilder
+    <T extends AbstractManagedChannelImplBuilder<T>> extends ManagedChannelBuilder<T> {
+
+  /**
+   * The default constructor.
+   */
+  protected AbstractManagedChannelImplBuilder() {}
+
+  /**
+   * This method serves to force sub classes to "hide" this static factory.
+   */
+  public static ManagedChannelBuilder<?> forAddress(String name, int port) {
+    throw new UnsupportedOperationException("Subclass failed to hide static factory");
+  }
+
+  /**
+   * This method serves to force sub classes to "hide" this static factory.
+   */
+  public static ManagedChannelBuilder<?> forTarget(String target) {
+    throw new UnsupportedOperationException("Subclass failed to hide static factory");
+  }
+
+  /**
+   * Returns the delegated {@code ManagedChannelBuilder}.
+   */
+  protected abstract ManagedChannelBuilder<?> delegate();
+
+  @Override
+  public T directExecutor() {
+    delegate().directExecutor();
+    return thisT();
+  }
+
+  @Override
+  public T executor(Executor executor) {
+    delegate().executor(executor);
+    return thisT();
+  }
+
+  @Override
+  public T offloadExecutor(Executor executor) {
+    delegate().offloadExecutor(executor);
+    return thisT();
+  }
+
+  @Override
+  public T intercept(List<ClientInterceptor> interceptors) {
+    delegate().intercept(interceptors);
+    return thisT();
+  }
+
+  @Override
+  public T intercept(ClientInterceptor... interceptors) {
+    delegate().intercept(interceptors);
+    return thisT();
+  }
+
+  @Override
+  public T userAgent(String userAgent) {
+    delegate().userAgent(userAgent);
+    return thisT();
+  }
+
+  @Override
+  public T overrideAuthority(String authority) {
+    delegate().overrideAuthority(authority);
+    return thisT();
+  }
+
+  @Override
+  public T usePlaintext() {
+    delegate().usePlaintext();
+    return thisT();
+  }
+
+  @Override
+  public T useTransportSecurity() {
+    delegate().useTransportSecurity();
+    return thisT();
+  }
+
+  @Deprecated
+  @Override
+  public T nameResolverFactory(NameResolver.Factory resolverFactory) {
+    delegate().nameResolverFactory(resolverFactory);
+    return thisT();
+  }
+
+  @Override
+  public T defaultLoadBalancingPolicy(String policy) {
+    delegate().defaultLoadBalancingPolicy(policy);
+    return thisT();
+  }
+
+  @Override
+  public T enableFullStreamDecompression() {
+    delegate().enableFullStreamDecompression();
+    return thisT();
+  }
+
+  @Override
+  public T decompressorRegistry(DecompressorRegistry registry) {
+    delegate().decompressorRegistry(registry);
+    return thisT();
+  }
+
+  @Override
+  public T compressorRegistry(CompressorRegistry registry) {
+    delegate().compressorRegistry(registry);
+    return thisT();
+  }
+
+  @Override
+  public T idleTimeout(long value, TimeUnit unit) {
+    delegate().idleTimeout(value, unit);
+    return thisT();
+  }
+
+  @Override
+  public T maxInboundMessageSize(int max) {
+    delegate().maxInboundMessageSize(max);
+    return thisT();
+  }
+
+  @Override
+  public T maxInboundMetadataSize(int max) {
+    delegate().maxInboundMetadataSize(max);
+    return thisT();
+  }
+
+  @Override
+  public T keepAliveTime(long keepAliveTime, TimeUnit timeUnit) {
+    delegate().keepAliveTime(keepAliveTime, timeUnit);
+    return thisT();
+  }
+
+  @Override
+  public T keepAliveTimeout(long keepAliveTimeout, TimeUnit timeUnit) {
+    delegate().keepAliveTimeout(keepAliveTimeout, timeUnit);
+    return thisT();
+  }
+
+  @Override
+  public T keepAliveWithoutCalls(boolean enable) {
+    delegate().keepAliveWithoutCalls(enable);
+    return thisT();
+  }
+
+  @Override
+  public T maxRetryAttempts(int maxRetryAttempts) {
+    delegate().maxRetryAttempts(maxRetryAttempts);
+    return thisT();
+  }
+
+  @Override
+  public T maxHedgedAttempts(int maxHedgedAttempts) {
+    delegate().maxHedgedAttempts(maxHedgedAttempts);
+    return thisT();
+  }
+
+  @Override
+  public T retryBufferSize(long bytes) {
+    delegate().retryBufferSize(bytes);
+    return thisT();
+  }
+
+  @Override
+  public T perRpcBufferLimit(long bytes) {
+    delegate().perRpcBufferLimit(bytes);
+    return thisT();
+  }
+
+  @Override
+  public T disableRetry() {
+    delegate().disableRetry();
+    return thisT();
+  }
+
+  @Override
+  public T enableRetry() {
+    delegate().enableRetry();
+    return thisT();
+  }
+
+  @Override
+  public T setBinaryLog(BinaryLog binaryLog) {
+    delegate().setBinaryLog(binaryLog);
+    return thisT();
+  }
+
+  @Override
+  public T maxTraceEvents(int maxTraceEvents) {
+    delegate().maxTraceEvents(maxTraceEvents);
+    return thisT();
+  }
+
+  @Override
+  public T proxyDetector(ProxyDetector proxyDetector) {
+    delegate().proxyDetector(proxyDetector);
+    return thisT();
+  }
+
+  @Override
+  public T defaultServiceConfig(@Nullable Map<String, ?> serviceConfig) {
+    delegate().defaultServiceConfig(serviceConfig);
+    return thisT();
+  }
+
+  @Override
+  public T disableServiceConfigLookUp() {
+    delegate().disableServiceConfigLookUp();
+    return thisT();
+  }
+
+  /**
+   * Returns the {@link ManagedChannel} built by the delegate by default. Overriding method can
+   * return different value.
+   */
+  @Override
+  public ManagedChannel build() {
+    return delegate().build();
+  }
+
+  @Override
+  public String toString() {
+    return MoreObjects.toStringHelper(this).add("delegate", delegate()).toString();
+  }
+
+  /**
+   * Returns the correctly typed version of the builder.
+   */
+  protected final T thisT() {
+    @SuppressWarnings("unchecked")
+    T thisT = (T) this;
+    return thisT;
+  }
+}