The tests are going to use it too

Generated by running protoc --objc_out=. --objcrpc_out=. *.proto in this directory.
Generates separate files until GeneratorContext::OpenForInsert/Append works.
A temporary podspec for the proto3 runtime is being used, pending the official.

So the root of the repository doesn’t have 2 podspecs.
All four libraries are subspecs now.
Adjusts the generated code to account for that.

The stub is manually adapted:

- to the evolved runtime,
- as if generated with insertion points.