Drop support for WebView for WPF and Winforms and default to WebView2

[frederikprijck]

Changes

Drop support for WebView on WPF and Winforms as this has been deprecated in favor of WebView2. We will now default to WebView2 on .NET Framework as well.

References

• https://www.nuget.org/packages/Microsoft.Toolkit.Wpf.UI.Controls.WebView
• https://www.nuget.org/packages/Microsoft.Toolkit.Forms.UI.Controls.WebView

Checklist

• [x] I have read the Auth0 general contribution guidelines
• [x] I have read the Auth0 Code of Conduct
• [x] All existing and new tests complete without errors
• [x] All code guidelines in the CONTRIBUTING documentation have been run/followed