Update to supported version of .net sdk 3.1.412, update C++ WinRT package, quite warnings, minor cleanup in XamlApplication

[ChrisGuzak]

Fixes #

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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
• [ ] 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

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[ghost]

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

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