Android annotations: implement new Symbol class

[fynngodau]

Android annotations API proposal implementation PR as a part of #1491. Closes #1493.

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• Symbol class is now usable.
• Updates should propagate correctly, except for icon updates in case a Symbol is attached to a manager directly.
• Existing tests for SymbolManager have been updated, and pass.
• To avoid conflicts, the following classes have temporary names that differ from their intended names:
  • Symbol → KSymbol
  • Annotation → KAnnotation
  • AnnotationContainer → KAnnotationContainer
• Some unresolved TODOs will be resolved later on.

[louwers]

Why are existing tests commented out?

These are only tests for functionality that was marked as deprecated, right?

[fynngodau]

@louwers I had to comment out the following classes:

• Circle, CircleManager, CircleManagerTest
• Line, LineManager, LineManagerTest
• Fill, FillManager, FillManagerTest

This was needed to make changes to AnnotationManager without adapting these classes (yet – since it is planned as a next step). Namely, AnnotationManager now deals with instances of KAnnotation and not AbstractAnnotation.

These classes have been commented out because they will be removed, but are still useful for reference in the next step:

• CircleOptions
• LineOptions
• FillOptions
• all subclasses of OnAnnotationClickListener, OnAnnotationLongClickListener, OnAnnotationDragListener (will be replaced with type aliases as well)

[louwers]

Thanks for the explanation @fynngodau, that makes sense.

@artakka Any chance you can help me review the Kotlin code added in this PR?

[artakka]

Some questions and suggestions, but overall looks good!

[fynngodau]

@artakka Thank you for reviewing. I have added b3c65a1 as a new commit to address your feedback; feel free to Resolve the remaining conversations above if you think everything is in order now.