Allow wallpaper to extend into the entire screen.

Previously it was constrained to displayInfo.appWidth/appHeight
which comes from PWM.getNonDecorDisplayWidth/Height, which includes
the nav bar.

Also adjust window layout to entire screen.

This allows wallpaper to extend into the navigation bar region,
important if the nav bar is hidden or transparent.

Bug:10505328
Change-Id: Ia6057b9c57b476a48f3b2d8b6368fd631e944a3e