Encourage using AndroidX instead of Android

[frederikprijck]

Changes

We offter two SDKs for Android:

• Auth0.OidcClient.Android
• Auth0.OidcClient.AndroidX

The difference relies in the support libraries used, where Auth0.OidcClient.Android uses deprecated support libraries which wont ever work on .NET6.

Therefore, going forward, our recommendation is to use Auth0.OidcClient.AndroidX, which work with both Xamarin and .NET Android.

Note that we aren't deprecating Auth0.OidcClient.Android yet, but we want to get everyone to Auth0.OidcClient.AndroidX.

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