Add isAutomaticReachabilityInBookModeEnabled config

To minimise disruption in experience, we disable automatic book mode
repositioning by default so letterboxed app will not jump to left side
of screen if device is half folded.

If app is centered in book mode, don't resize bounds to split screen
aspect ratio. Only resize if app is on left/right size when half folded.

Fix: 270560857
Test: Manual && atest WmTests:SizeCompatTests

Change-Id: Ifc259c1c2a5ad37c5714c359bc090274b7bcb565