Keep custom keep-clear Rects if preferKeepClear is set

Since ViewParents can be set to not clip their children, custom
keep clear areas can extend beyond the bounds of its hosting View.
If preferKeepClear is set, add the View's bounds as a keep clear area,
but also keep the custom Rects.

Bug: 221073574
Test: atest KeepClearRectsTests
Change-Id: I85a4e4a223fbba787c5afebf2689a031243808d4