Automatic merge from submit-queue

Generate a better Stringer method for proto types

This replaces the bad string output generated by golang/proto with gogo/protobuf stringer generation. Makes the output similar to %#v and more debuggable. We have to have a String() method to implement proto.Message, so this is strictly better.

@wojtek-t, @thockin for after your PR merges

Fixes #28756