Don't apply nav bar insets in tablets

- With flexible inset changes in T, taskbar is no longer inseted in getCurrentSizeRange, i.e. DeviceProfile.availableHeight no longer inset nav bar size
- In order for home screen sizes to be calcualted correctly, avoid inseting nav bar in LauncherRootView
- Only apply a bottom padding with stashed taskbar size to necessarily surfaces (Overview)
- Home screen icon overlap will be fixed in separate CL

Bug: 215528237
Test: maual in tablet gesture nav and 3 buttons
Change-Id: I9bc796ba059159e819f8cd121ddabab96c8113d2