Expose TimeTraceProfiler for Async Events (#83778)

To avoid issue like https://github.com/llvm/llvm-project/issues/56554
and https://github.com/llvm/llvm-project/issues/83236 due to no
guarantees for nested relationships between file level span and syntax
tree level span, I'd like to have a `timeTraceAsyncProfilerBegin`
specific to trace handling only `Source` spans around

https://github.com/llvm/llvm-project/blob/8715f256911786520bb727ce067098d7082ac45c/clang/lib/Sema/Sema.cpp#L153-L170.

This is a preparation PR to do that in [following
PR](https://github.com/llvm/llvm-project/pull/83961).