Using DispatcherQueue instead of CoreDispatcher

[azchohfi]

Fixes #3803

Some classes were still using CoreDispatcher.

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

Some classes are not working properly on Xaml Islands

What is the new behavior?

We don't use the old Dispatcher anymore. Everything is using DispatcherQueue and/or DispatcherQueueTimer.

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Pull Request has been submitted to the documentation repository instructions. Link:
• Sample in sample app has been added / updated (for bug fixes / features)
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• New major technical changes in the toolkit have or will be added to the Wiki e.g. build changes, source generators, testing infrastructure, sample creation changes, etc...
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes

[ghost]

Thanks azchohfi for opening a Pull Request! The reviewers will test the PR and highlight if there is any conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌