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]

Please sync with main which now has https://github.com/microsoft/TemplateStudio/issues/4640.

Also please resolve the below test failure.

At least one file (../../../../TemplateStudioForWinUICs/Templates\Pg\WebView\ViewModels\Param_ItemNameViewModel.cs) is not encoded correctly. Ensure all template files are encoded correctly with the script at '_utils/Set-All-Text-File-Template-Encodings.ps1'\r\nExpected: True\r\nActual:   False

[mrlacey]

@humbertomoli99 the changes you need to get this merged are at https://github.com/microsoft/TemplateStudio/compare/main...mrlacey:WindowsTemplateStudio:i4639-update?diff=split