Add WindowInsets#getBoundingRects APIs

Adds:
1) getBoundingRects(): to obtain the rectangles within Insets that are
partially or fully obscuring the window
2) getFrame(): to query the size of the window during WindowInsets
updates
3) WCT#addInsetsSource w/boundingRects param: for sources (e.g. WM
Shell's caption bar) to specify the bounding rects.

Bug: 316387515
Flag: ACONFIG android.view.flags.customizable_window_headers DEVELOPMENT
Test: atest InsetsSourceTest WindowInsetsTest InsetsStateTest
WindowDecorationTests WindowOrganizerTests

Change-Id: If044d67e0614b9ca336169487b54b04004394066