Depends on D81998
Hmm, I like the idea of avoiding a custom type and just reusing the standard one here, but:
anything wrong with just std::function<ClangTidyOptions(StringRef)>?
I'm of the idea that rather than having ClangdTidyOptionsProvider inherit form tidy::ClangTidyOptionsProvider, just have it as its own class. We don't need the interface offered by clang tidy here. It would solve the must be threadsafe comment issue as well as reduce the need for some unnecessary code in there.