Supersedes !7928 with some test tweaks:
* Test that shutdown waits for any queued handler,
* Use message loop only when necessary (DQTYPE_THREAD_CURRENT),
* Remove some non-deterministic refcount checks after shutdown, as dispatch thread might still hold some until it exits.
--
v2: coremessaging: Partially implement CreateDispatcherQueueController().
coremessaging/tests: Add CreateDispatcherQueueController() tests.
coremessaging/tests: Add IDispatcherQueueControllerStatics::CreateOnDedicatedThread() tests.
coremessaging: Add IDispatcherQueueControllerStatics stub.
https://gitlab.winehq.org/wine/wine/-/merge_requests/8055