Xamarin version of the ExoPlayer bindings

[janwiebe-jump]

:sparkles: What kind of change does this PR introduce? (Bug fix, feature, docs update...)

As suggested in #145 the Xamarin version should be in separate packages. I prepared this by incorporating the changes of @ArchangelWTF in #145 into a xamarin branch that I would like to target to a new branch in this repository.

:arrow_heading_down: What is the current behavior?

No recent Android 12/13 support

:new: What is the new behavior (if this is a feature change)?

Project is built against MonoAndroid12.0 and 13.0

:boom: Does this PR introduce a breaking change?

:bug: Recommendations for testing

:memo: Links to relevant issues/docs

:thinking: Checklist before submitting

• [X] All projects build
• [x] Follows style guide lines
• [X] Relevant documentation was updated
• [X] Rebased onto current develop

[martijn00]

https://www.nuget.org/packages/Xam.Plugins.Android.ExoPlayer/2.18.9-xamarin.1

The xamarin branch is working now. If you're missing any binding fixes, can you open a PR for that?