[clang] [clang][frontend] Add support for attribute plugins for statement attributes (PR #110334)

[Ilya Biryukov via cfe-commits]

ilya-biryukov wrote:

This looks like a relatively straightforward extension in line with the current Clang interfaces. Therefore, I feel we should accept this.

However, please wait for feedback from Clang owners to make sure this does not go against some non-obvious trade-offs or future plans that Clang has.

cc @AaronBallman, @cor3ntin 

https://github.com/llvm/llvm-project/pull/110334