Bug: Using a non-reentrant wait synchronization context causes app to hang on exit

Description

For more context see https://github.com/microsoft/CsWinRT/issues/2422. Basically, the issue is if I subclass DispatcherQueueSynchronizationContext to use a non-reentrant wait to avoid reentrancy issues in WindowsAppSDK, then the app hangs on exit. There is an easy workaround which is to revert to the standard wait on FrameworkShutdownStarting. However, it would be nice if this wasn't needed. I'm posting here now in case this reqires any .net runtime updates before v11 is released.

Steps To Reproduce

Use this code in app startup where CustomDispatcherQueueSynchronizationContext is given in https://github.com/microsoft/CsWinRT/issues/2422 (and remove the workaround when shutting down).

Application.Start((p) => {
    var context = new CustomDispatcherQueueSynchronizationContext(DispatcherQueue.GetForCurrentThread());
    SynchronizationContext.SetSynchronizationContext(context);
    _ = new App();
});

Expected Behavior

No hang on exit

Version Info

Last tested on CsWinRT 2.2, WindowsAppSDK 2.0

Additional Context

No response

Start with the CustomDispatcherQueueSynchronizationContext example in CsWinRT issue #2422 and the Application.Start setup shown here. Reproduce the hang using the non-reentrant wait without the FrameworkShutdownStarting workaround, then trace shutdown behavior. Done means the app exits without hanging while retaining the non-reentrant wait.