[clang] [llvm] Added instant events and marking defered templated instantiation. (PR #103039)

[Ilya Biryukov via cfe-commits]

https://github.com/ilya-biryukov commented:

I have left quite a few comments, but they are mostly about the code style.
I think this looks really good overall and almost ready to land.

Could you split the change to Sema into a separate PR so that we have time profiler changes separately?

https://github.com/llvm/llvm-project/pull/103039