Support detached Fragments by removing references to the Activity

[jimmithy]

🎯 Goal

Previously if we create a fragment that is not yet attached to the activity and reference the balloon, this will throw an IllegalStateException. This is because the lazy loader requires an Activity even thought the implementation only requires Context.

This change removes all references to activities, so the balloon can be successfully attached to the anchor without needing the activity context.

🛠 Implementation details

1. Update Lazy helpers to use requireContext instead of requireActivity
2. Remove unused getActivity method
3. Remove unneccesary Context.isFinishing method because isAttachedToWindow should resolve issue android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running? #92

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[skydoves]

Hey @jimmithy, checking out the isFinishing is needed for working correctly with Activity. I'm wondering if you can resolve this issue by calling the show method inside the If statements, which has isAttachedToWindow as a condition.