cherrypick restoration of mutableCopy helpers

java/core/src/main/java/com/google/protobuf/GeneratedMessageV3.java

@@ -10,6 +10,11 @@
 import com.google.protobuf.Descriptors.Descriptor;
 import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.Descriptors.OneofDescriptor;
+import com.google.protobuf.Internal.BooleanList;
+import com.google.protobuf.Internal.DoubleList;
+import com.google.protobuf.Internal.FloatList;
+import com.google.protobuf.Internal.IntList;
+import com.google.protobuf.Internal.LongList;
 import java.util.List;
 
 /**
@@ -36,6 +41,46 @@ protected GeneratedMessageV3(Builder<?> builder) {
     super(builder);
   }
 
+  /* @deprecated This method is deprecated, and slated for removal in the next Java breaking change
+   * (5.x). Users should update gencode to >= 4.26.x which uses makeMutableCopy() instead.
+   */
+  @Deprecated
+  protected static IntList mutableCopy(IntList list) {
+    return makeMutableCopy(list);
+  }
+
+  /* @deprecated This method is deprecated, and slated for removal in the next Java breaking change
+   * (5.x). Users should update gencode to >= 4.26.x which uses makeMutableCopy() instead.
+   */
+  @Deprecated
+  protected static LongList mutableCopy(LongList list) {
+    return makeMutableCopy(list);
+  }
+
+  /* @deprecated This method is deprecated, and slated for removal in the next Java breaking change
+   * (5.x). Users should update gencode to >= 4.26.x which uses makeMutableCopy() instead.
+   */
+  @Deprecated
+  protected static FloatList mutableCopy(FloatList list) {
+    return makeMutableCopy(list);
+  }
+
+  /* @deprecated This method is deprecated, and slated for removal in the next Java breaking change
+   * (5.x). Users should update gencode to >= 4.26.x which uses makeMutableCopy() instead.
+   */
+  @Deprecated
+  protected static DoubleList mutableCopy(DoubleList list) {
+    return makeMutableCopy(list);
+  }
+
+  /* @deprecated This method is deprecated, and slated for removal in the next Java breaking change
+   * (5.x). Users should update gencode to >= 4.26.x which uses makeMutableCopy() instead.
+   */
+  @Deprecated
+  protected static BooleanList mutableCopy(BooleanList list) {
+    return makeMutableCopy(list);
+  }
+
   /* Overrides abstract GeneratedMessage.internalGetFieldAccessorTable().
    *
    * @deprecated This method is deprecated, and slated for removal in the next Java breaking change