[Feature Request] Move/remove third party protos to a separate place instead of root

[cretz]

Describe the solution you'd like

Other users protoc from the root of this repo. When 108b40a was done, we put google-based proto dependencies at the same path as our own assuming that all users were ok with using these google protos instead of their own (e.g. from https://github.com/protocolbuffers/protobuf/tree/main/src/google/protobuf).

We probably need to either:

• Put the third party references where the protoc is actually run (e.g. api-go) and only embed them here when testing

or:

• Move google/api to thirdparty/google-api/google/api
• Move google/protobuf to thirdparty/google-protobuf/google/protobuf
• Add -I thirdparty/google-api and -I thirdparty/google-protobuf to our protoc
• Confirm the fact that thirdparty is nested under our root is ok and can easily be ignored by most protoc use