[clang] [clang] Factor out OpenACC part of `Sema` (PR #84184)

[via cfe-commits]

https://github.com/cor3ntin commented:

I have mixed feelings about that.

One one hand, i appreciate efforts to decouple Sema, on the other hand It's unclear to me how much benefit we will be able to realize.

I think I'm fine with the change as long as there is no attempt to remove everything.
Ie, I think C and C++ and common functionality should stay directly under sema.

Some C++-specific functions might not need to be member function so if we wanted to cut dependencies I'd rather explore than.

I think we want `SemaOpenACC` to inherit from a common base class that would provide getAstContext, Diag, and other super commonly used functions directly.



https://github.com/llvm/llvm-project/pull/84184