Bring task to front when we can't move to adjacent stack

If task was requested to move to adjacent stack with mLaunchStackId set
and FLAG_ACTIVITY_LAUNCH_ADJACENT not set - we don't move it from its
current stack. If the task was covered with other task(s) it wouldn't
be brought to front.
This CL checks if mLaunchStackId is provided and is a valid stack for this
task, then we move it to front of current stack as a safer option.

Bug: 29103549
Change-Id: I3065960f082cfbf9a5b43c6e83b5cebe3dd69df6