The `try await` ordering is both easier to read and indicates the order
of operations better, because the suspension point occurs first and
then one can observe a thrown error.
Bridging an async Swift method back to an ObjC completion-handler-based API requires
that the ObjC thunk spawn a task on which to execute the Swift async API and pass
its results back on to the completion handler.
So if we use an ObjC imported as async to conform to a Swift protocol, delegate a Swift subclass initializer, etc.,
we generate the conversion thunk to the Swift calling convention for the imported API.
