OnMapReadyCallback invoked when view is unmeasured

[tobrun]

Since the 4.2.0 release we are using DID_FINISH_LOADING_STYLE as event to invoke the OnMapReadyCallback. An issue noticed is that there are situations that the DID_FINISH_LOADING_STYLE event is emitted before the MapView is even measured. This currently results in using width 0 in some calculations (eg. #6769). I think we should take in account if the view is actually measured before providing the user the MapboxMap.

A way to listen if a View is measured is using a OnGlobalLayoutListener.

[tobrun]

Picking this up as part of #7736, for that refactor I'm required to move initialization of the map object and postpone other initializations. I'm hoping that as a side effect this will result in the view being already measured when we initialize, else we need to look into including OnGlobalLayoutListener as part of the initialization.