Keep insets stable when taskbar is destroyed/recreated

- Calculate nav bar insets ourselves. Currently when taskbar is going to be present, we use taskbarSize as the nav bar insets. This is consistent with other existing calculations, but going forward we should instead always use the nav bar size instead of taskbar size, given we don't want taskbar to inset launcher (since taskbar is hidden).
- Also update tappable insets to be 0 in gesture mode. Test: Swipe to all apps, ensure there's no background protection at the bottom.

Test: Rotate device, no visual jumps
Test: Stash taskbar, quick switch a couple times without settling, and swipe up to overview; no jank due to reapplyState()

Bug: 198798034
Fixes: 197232424
Fixes: 197212581
Change-Id: I4c2bb5816dbb214846bd9f2a46c6f759c0545911