chore: import upstream snapshot with attribution

tools/add_syntax_equal_proto2_to_all.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You 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.
+
+# Add 'syntax="proto2";' to the beginning of all proto files under 
+# PWD(recursively) if the proto file does not have it.
+for file in $(find . -name "*.proto"); do
+    if grep -q 'syntax\s*=\s*"proto2";' $file; then
+        echo "[already had] $file";
+    else 
+        sed -i '1s/^/syntax="proto2";\n/' $file
+        echo "[replaced] $file"
+    fi
+done