[Clang] Do not emit exception diagnostics from coroutines and coroutine lambdas

All exceptions thrown in coroutine bodies are caught and
unhandled_exception member of the coroutine promise type is called.
In accordance with the existing rules of diagnostics related to
exceptions thrown in functions marked noexcept, even if the promise
type's constructor, get_return_object, or unhandled_exception
throws, diagnostics should not be emitted.

Fixes #48797.

Differential Revision: https://reviews.llvm.org/D144352