[protobuf] Load C++,Java,Protobuf rules from Starlark

Cherry-pick of: protocolbuffers/protobuf#6432 and protocolbuffers/protobuf#6445

third_party/protobuf/3.6.1/BUILD

@@ -1,5 +1,9 @@
 # Bazel (http://bazel.io/) BUILD file for Protobuf.
 
+load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library", "cc_test", "objc_library")
+load("@rules_java//java:defs.bzl", "java_library")
+load("@rules_proto//proto:defs.bzl", "proto_lang_toolchain", "proto_library")
+
 licenses(["notice"])
 
 exports_files(["LICENSE"])

third_party/protobuf/3.6.1/protobuf.bzl

@@ -1,4 +1,4 @@
-# Needed for #9006. Hopefully a future upstream version will include this line.
+load("@rules_cc//cc:defs.bzl", "cc_library")
 load("@rules_python//python:defs.bzl", "py_library", "py_test")
 
 def _GetPath(ctx, path):
@@ -227,7 +227,7 @@ def cc_proto_library(
         )
 
         # An empty cc_library to make rule dependency consistent.
-        native.cc_library(
+        cc_library(
             name = name,
             **kargs
         )
@@ -259,7 +259,7 @@ def cc_proto_library(
     if use_grpc_plugin:
         cc_libs = cc_libs + ["//external:grpc_lib"]
 
-    native.cc_library(
+    cc_library(
         name = name,
         srcs = gen_srcs,
         hdrs = gen_hdrs,

third_party/protobuf/3.6.1/util/python/BUILD

@@ -1,3 +1,5 @@
+load("@rules_cc//cc:defs.bzl", "cc_library")
+
 # This is a placeholder for python headers. Projects needing to use
 # fast cpp protos in protobuf's python interface should build with
 # --define=use_fast_cpp_protos=true, and in addition, provide