Fixes for increased usage of light navigation bar

- Fix an issue where IME doesn't really cover nav area but still
became window to deterine light navigation.
- Only invert nav bar icons when expanding the shade if the scrim
is dark.
- Fix logic such that status bar always becomes the window to
dermine light nav bar on lockscreen.

Test: Open shade with light nav
Test: Open Keyguard in landscape in all apps
Test: Unlock phone with light nav

Change-Id: If024a8b81942a6675243b703c0509cd88de8d932
Fixes: 63539478
Fixes: 63533427
Fixes: 63577858