Improve documentation for Xamarin Android ownerWindow and improve exception with null ownerWindow

[jennyf19]

Documentation Related To Component:

In Msal v3, developers must pass in an Activity for the ownerWindow on Android.
For example:

result = await App.MsalPublicClient.AcquireTokenInteractive(App.Scopes, App.AndroidActivity).ExecuteAsync();

However, if null is passed in to the ownerWindow, the following error is thrown:
Unhandled Exception: System.PlatformNotSupportedException: Possible Cause: If you are using an XForms app, or generally a netstandard assembly, make sure you add a reference to Microsoft.Identity.Client.dll from each platform assembly (e.g. UWP, Android, iOS), not just from the common netstandard assembly

The error should be something like:
On the Android platform the ownerWindow cannot be null. An Activity must be passed to the ownerWindow in the AcquireTokenInteractive Call. Please see https://aka.ms -something cool for more details and a code sample

Please check those that apply

• typo
• documentation doesn't exist
• documentation needs clarification
• error(s) in example
• needs example

See related issue

[jmprieur]

@jennyf19 the fact that the exception is not explicit seems a bug as well?
cc: @henrik-me ?

[bgavrilMS]

I think this is a duplicate of #918 but I agree that the exception also needs to be fixed.

[jennyf19]

confirmed that when passing in a null ownerWindow on Android, we throw a correct exception w/a clear error message: InvalidOperationException: Activity is required for parent object on Android.

Closing, as I think @bgavrilMS is right and the second part of this issue is a duplicate.