[CIR] Emit ready and suspend branches for cir.await (#168814)
This PR adds codegen for `cir.await` ready and suspend. One notable
difference from the classic codegen is that, in the suspend branch, it
emits an `AwaitSuspendWrapper`(`.__await_suspend_wrapper__init`)
function that is always inlined. This function wraps the suspend logic
inside an internal wrapper that gets inlined. Example here:
https://godbolt.org/z/rWYGcaaG4