Move `protobuf_test_util.cc` into a common location for all tests that use protobuf

[alinaliBQ]

Describe the enhancement requested

In #14508 (comment), it was proposed that google::protobuf::ShutdownProtobufLibrary should be called after all tests that use protobuf.

We should move protobuf_test_util.cc into a more common location so all tests that use protobuf can bring this file and safely shut down the protobuf library.

Component(s)

C++