Summary: @public When Android dispatches `MotionEvent` to `ReactRootView`, it needs to find a correspoding react node that should receive it. To be able to do it, we need to store boundaries of every `FlatShadowNode` in `FlatViewGroup`. Then we can iterate over node boundaries and find one that contains the touch event coordinates.
Reviewed By: sriramramani
Differential Revision: D2694197
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