Don’t relaunch activity in fullscreen stack when entering split screen mode

When entering split-screen mode by long pressing the recents button, the
top task in the fullscreen stack is moved to the docked stack and the new
top task is the fullscreen stack is considered visible for a short amount
of time until sys-ui launches the recents activity. This causes the new
top activity in the fullscreen stack to be relaunched due to configuration
change.
To fix this sys-ui now sends an hint to activity manager to move the home
stack forward so that it can be on-top of the fullscreen stack and makes
it invisible before recent is launched and animated in.

Bug: 28470261
Change-Id: Icfd85e932fe913dfb498752b5878cc7c690fd559