Revert "Replaced all instances of Simple{IDF}toa with StrCat."
Revert "Replaced all instances of Simple{IDF}toa with StrCat."

This reverts commit 9b8eeecf7d3809926532b2b9ff7d20f4e37f9b87.

protocolbuffers/protobuf-javascript,protocolbuffers/protobuf-javascript,protocolbuffers/protobuf-javascript,protocolbuffers/protobuf-javascript