api:stabilize offloadExecutor. (#9931)

* api:Stabalize offloadExecutor.

fixes #6279

Author: larry-safran

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

@@ -119,7 +119,6 @@ public static ManagedChannelBuilder<?> forTarget(String target) {
    * @throws UnsupportedOperationException if unsupported
    * @since 1.25.0
    */
-  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/6279")
   public T offloadExecutor(Executor executor) {
     throw new UnsupportedOperationException();
   }

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

@@ -366,7 +366,6 @@ public ChannelLogger getChannelLogger() {
      * @since 1.25.0
      */
     @Nullable
-    @ExperimentalApi("https://github.com/grpc/grpc-java/issues/6279")
     public Executor getOffloadExecutor() {
       return executor;
     }
@@ -510,7 +509,6 @@ public Builder setChannelLogger(ChannelLogger channelLogger) {
        *
        * @since 1.25.0
        */
-      @ExperimentalApi("https://github.com/grpc/grpc-java/issues/6279")
       public Builder setOffloadExecutor(Executor executor) {
         this.executor = executor;
         return this;