[llvm] Lift raw_socket_stream implementation out into own files (PR #75653)

[Michael Spencer via llvm-commits]

https://github.com/Bigcheese approved this pull request.

There's also an include of `llvm/Support/Threading.h` in `raw_ostream.h` you should move to the new header.

Looks good with these changes assuming the tests pass.

https://github.com/llvm/llvm-project/pull/75653