Fix Launcher3 tests for tablets

- Consider taskbar size for bottom gesture size, by using TargetInsets
- TargetInsets should substract overlapping taskbar size when it's present
- For pressHome, use the same gesture scope when context menu is present as well.
- For pressHome, GestureScope.INSIDE_TO_OUTSIDE should only be used when it's already at home screen on launcher3 tablet.

Bug: 193539246
Test: NexusLauncherTest and Launcher3Test
Change-Id: I4a20522f3b38ef326acae4b189df11a125990411