Support: Change InMemoryFileSystem::addFileNoOwn to take a MemoryBufferRef, NFC

Found this by chance when looking at the InMemoryFileSystem API, seems
like an easy cleanup.

Differential Revision: https://reviews.llvm.org/D90893

GitOrigin-RevId: e763e032f8bbf5a4da60d099b1df4cd16e44e139
1 file changed