Use the largest display size when calculating wallpaper crop size

Make sure we always use the same display size when calculating cropping for
static wallpapers if there's more than one display, specifically use the
largest screen

(Note: there's still some discrepancies between preview and actual
wallpaper that we need to sort out in a follow-up CL)

Bug: 195120817
Test: manual
Change-Id: I4ccdc55bcb28e417f9fd11b082dca92cc9688055
7 files changed