Only use simple rects for cutout region

Otherwise there is a big performance hit in all kinds of
situations where we do operations with the region, specifically
when:

- updating input windows
- insetting the cutout during layout
- touch dispatch

Test: DisplayCutoutTest, WmDisplayCutoutTest
Bug: 110464019
Bug: 110452325
Change-Id: I94a25c3794ecd33b8b7204ca308ac91623498f13