apacheGH-34692: [Java] Expose Location.toSocketAddress (apache#34648)

### Rationale for this change

### What changes are included in this PR?

Change `Location.toSocketAddress()` to a public method. This is useful for creating a `FlightClient` via `FlightGrpcUtils.createFlightClient`:

https://github.com/apache/arrow/blob/08fb86107b001e2e1903ae0e416ff51386d4239e/java/flight/flight-grpc/src/main/java/org/apache/arrow/flight/FlightGrpcUtils.java#L148

### Are these changes tested?

### Are there any user-facing changes?

* Closes: apache#34692

Authored-by: Jie Zhang <zhangjie@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>

java/flight/flight-core/src/main/java/org/apache/arrow/flight/Location.java

@@ -60,7 +60,7 @@ public URI getUri() {
    *
    * @return null if could not be converted
    */
-  SocketAddress toSocketAddress() {
+  public SocketAddress toSocketAddress() {
     switch (uri.getScheme()) {
       case LocationSchemes.GRPC:
       case LocationSchemes.GRPC_TLS:

java/flight/flight-core/src/test/java/org/apache/arrow/flight/TestBasicOperation.java

@@ -24,6 +24,7 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.net.InetSocketAddress;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.nio.charset.StandardCharsets;
@@ -413,6 +414,24 @@ public void testProtobufSchemaCompatibility() throws Exception {
     }
   }
 
+  @Test
+  public void testGrpcInsecureLocation() throws Exception {
+    Location location = Location.forGrpcInsecure(LOCALHOST, 9000);
+    Assertions.assertEquals(
+        new URI(LocationSchemes.GRPC_INSECURE, null, LOCALHOST, 9000, null, null, null),
+        location.getUri());
+    Assertions.assertEquals(new InetSocketAddress(LOCALHOST, 9000), location.toSocketAddress());
+  }
+
+  @Test
+  public void testGrpcTlsLocation() throws Exception {
+    Location location = Location.forGrpcTls(LOCALHOST, 9000);
+    Assertions.assertEquals(
+            new URI(LocationSchemes.GRPC_TLS, null, LOCALHOST, 9000, null, null, null),
+            location.getUri());
+    Assertions.assertEquals(new InetSocketAddress(LOCALHOST, 9000), location.toSocketAddress());
+  }
+
   /**
    * An example FlightProducer for test purposes.
    */