HeadsUpManagerPhone handles adding extra touchable region for the
display cutout. When this changed to use Rects, the extra touch region
was applied to the entire phone width because Rect#union() will cause
the resulting Rect to grow in every dimension. The fix is to use a
Region instead so we can properly union only the space under the notch
Fixes: 135487528
Test: manual
Change-Id: I1d39785087cc3378fc42363df170b81b84420a8e
e1822fd8d4