Update Dispatcher/DispatcherTimer references to DispatcherQueue/DispatcherQueueTimer

[michael-hawker]

Describe the bug

We need to move off Dispatcher and DispatcherTimer so that controls can work in XAML Islands and WinUI 3. Looks like we have missed some references to the prior work we did at the start of 7.0.

Expected behavior

No longer use Dispatcher and DispatcherTimer. Use DispatcherQueue and DispatcherQueueTime instead.

FYI @azchohfi