using community toolkit mvvm in viewmodel of webview

[humbertomoli99]

PR checklist

Quick summary of changes

Which issue does this PR relate to?

Applies to the following platforms:

• [x] WinUI
• [ ] WPF
• [ ] UWP

Anything that requires particular review or attention?

Do all automated tests pass?

Have automated tests been added for new features?

If you've changed the UI:

• Be sure you are including screenshots to show the changes.
• Be sure you have reviewed the accessibility checklist.

If you've included a new template:

• Be sure you reviewed the Template Verification Checklist.
• Be sure it's included in the list on this UWP or WPF getting started doc.

Have you raised issues for any needed follow-on work?

Have docs been updated?

If breaking changes or different ways of doing things have been introduced, have they been communicated widely?

[mikebattista]

Thanks!