[flutter_local_notifications] Add support to pass bubble activity + intent to notification

[Airyzz]

This allows for use of Android conversation bubbles api

[Levi-Lesches]

Interesting! Perhaps you can make another Dart class for the bubble details? That way they stay bundled together and you can just use ?. to check its members instead of checking each one independently (eg, what happens if bubbleActivity == null && bubbleExtra != null? This way you can just make AndroidBubble.activity be required and AndroidBubble.extra be nullable).

Then be sure to properly handle the error case in your Java code.

And of course, please be sure to document the Dart parts, any extra Android-specific setup, and add a test case if possible, and let us know when you're finished. I'd be happy to test on my end as well.