Allows support for other default browsers on Android to work with the Web Authenticator

[vhugogarcia]

Description of Change

When a browser different from Chrome is assigned as default in Android, the web authenticator throws an exception with some browsers only.
This change prevents NullReferenceException on WebAuthenticatorIntermediateActivity.android.cs and allows support for other default browsers on Android to work with the Web Authenticator, and continue the authentication flow.

This change has been tested with the following browsers:

• Firefox,
• Microsoft Edge
• Chrome
• DuckDuckGo
• Mi Browser
• Samsung Internet
• Opera
• Brave.

Important: *Due to a browser limitation, some browsers do not support Android CustomTabs feature to get back to the app automatically, so, the user must manually hit the back button or open again the app (Opera and Mi Browser). This is something that cannot be managed in .NET MAUI.

Issues Fixed

Fixes #13798

[ghost]

Hey there @vhugogarcia! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[MartyIX]

Suggested change

	if (actualIntent != null && !launched)
	if (actualIntent is not null && !launched)

[mattleibow]

Thanks for this PR - we actually found a bigger issue. Using the system browser should NOT trigger the intermediate activity at all. @Redth fixed the root in #15187

[vhugogarcia]

Thanks @mattleibow for the heads-up. Happy to see it has been fixed fully. Please back-port that issue to .NET MAUI 7 service release. We are facing this issue with our apps and it will be good 🙏 to have it fix.

Thanks again 😎