[clang] [Clang] Coroutines: Properly Check if `await_suspend` return type is a `std::coroutine_handle` (PR #85684)

[Yuxuan Chen via cfe-commits]

yuxuanchen1997 wrote:

@ChuanqiXu9 

I have updated the patch to check for `std::coroutine_handle<P>` and does not rely on `SemaExprCXX` changes. Please let me know what you think. 

https://github.com/llvm/llvm-project/pull/85684