swipe-dismiss: set up gesture exlcusion for explicit windowSwipeToDismiss=false

WindowOnBackInvokedDispatcher:
- Convert binary Checker to tri-state so that we can determine if
  windowSwipeToDismiss=false is explicitly set.
- Other minor refactor.

ViewRootImpl:
- Set window frame as root system gesture exclusion rect if
  windowSwipeToDismiss=false is explicitly set & not opt-in.

Test: manual, validate mSystemExclusion set
Test: on phone: http://shortn/_wOryjDg8aB
Test: on watch: http://shortn/_mPypnw2Ibt
Bug: 290801678
Bug: 291531205
Change-Id: Ie7d925869fad25b3f7599d388c0e7ae5ef6fef53