Changes:
- Renamed all references of something_cc_proto to something_portable_proto.
- Added //cc/util/protobuf_helper which creates a namespace portable_port that maps to the correct namespace.
- Replaced all deps to //net/proto2/ with //cc/util:protobuf_helper.
- Replaced all instances of the proto2:: namespace with portable_proto::
- Deleted the line 'namespace util = crypto::tink::util' because it was conflicting with //util/task/status.h (a dependency of portable_proto_lib). Also, it wasn't really used in any of the files.

Notes:
- When adding a new proto you will need to whitelist it in proto/portable_tink_filter.asciipb
- For google3 (BUILD) we should use portable_proto_lib, for opensource (BUILD.bazel) we should use cc_proto_lib.
PiperOrigin-RevId: 193084414
GitOrigin-RevId: 266a0dbb7f66549655e521350b70b10d4a872286