[clang] [Clang] Coroutines: Properly Check if `await_suspend` return type convertible to `std::coroutine_handle<>` (PR #85684)

[Yuxuan Chen via cfe-commits]

yuxuanchen1997 wrote:

> I am confused. If we don't need to check whether a type can be converted to std::coroutine_handle, why do we still need EvaluateBinaryTypeTraits or similar things.

I thought your previous comment was to show concern about exposing `EvaluateBinaryTypeTraits` contained a bunch of nonfunctional changes. Do you think it's good?

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