[Bug] WAM is invoked for B2C authorities and MSAL.Desktop API is not good for B2C

[bgavrilMS]

1. Use sample https://github.com/Azure-Samples/active-directory-b2c-dotnet-desktop
2. Add MSAL.Desktop package and install it

.AddDesktopFeatures(BrokerOptions.Windows)

Expected: webview2 support for b2c
Actual: WAM is invoked and it fails

Proposed solution:

1. Fallback from WAM to browser on B2C
2. Add explicit API for WebView support, because WithDesktopFeatures(new BrokerOptions(Windows)) is not great
3. Allow WebView2 on ADFS (no COGS implication for poor SSO)

[bgavrilMS]

CC @neha-bhargava as ICM follow up

[rayluo]

If we haven't already, we shall also disable WAM for ADFS. Both B2C and ADFS were documented as the fallback scenarios in our internal design docs.