Add SourceFile type for CodeGenLib

Sources/GRPCCodeGen/SourceFile.swift

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2023, gRPC Authors All rights reserved.
+ *
+ * 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.
+ */
+
+/// Representation of the file to be created by the code generator, that contains the
+/// generated Swift source code.
+public struct SourceFile: Sendable, Hashable {
+  /// The base name of the file.
+  public var name: String
+
+  /// The generated code as a String.
+  public var contents: String
+
+  /// Creates a representation of a file containing Swift code with the specified name
+  /// and contents.
+  public init(name: String, contents: String) {
+    self.name = name
+    self.contents = contents
+  }
+}