[clang] [llvm] [clang][ssaf] Add the TUSummaryExtractorRegistry (PR #173290)

[Tomohiro Kashiwada via cfe-commits]

kikairoya wrote:

> Hey, I'm not available for the next 24 hours, but if you have a fix then I'm happy to review.
> Thanks for the guidance, your insight was really valuable.

#176730
Submitted.
There's no rush, but I'd appreciate it if you could review and merge it (I have no permission) when you have time.

https://github.com/llvm/llvm-project/pull/173290