Address some insets issues in Taskbar All Apps

- Don't report insets change to underlying app when stashing taskbar during all apps transition
- Internally override all apps insets to take stashing into account
- Don't offset all apps window by display cutouts, as we handle them internally via padding internally
- Also Fix bug where "stashing" taskbar in 3 button mode (which just fades out taskbar icons but keeps nav buttons) was reporting smaller insets to apps

Test: 1) open all apps in Calculator, ensure Calculator doesn't adjust insets and all apps has bottom content padding but no nav scrim
2) in 3 button mode, scroll to bottom of all apps and can read last row icon labels
3) enable display cutout in developer options, ensure no change to tests 1 and 2, and all apps scrim fills the screen (including behind cutout)
Fixes: 219980805

Change-Id: Ic3c6a744bc675e4ea277d22c4c0b3b353eddd905