Protoutil

These files were copied as-needed from https://chromium.googlesource.com/infra/luci/luci-py/+/9ed10cfbc7deccf4c4398dd76526332dc09f1a83/appengine/components/components/protoutil/. This is needed to parse text format LUCI configs, which is done both by code luci-py and in this repo. Ideally we‘d share the code without copying but there’s no good way to do that.