Fix z-order of displays when adjusting position of stack

When moving a stack to top including its parent (display),
if the target position is adjusted to non-top because there
is other always-on-top stack in this container, the display
should also be moved to top for higher focus priority.

Z-order
Top          |----------------|
   Display 1 | [Normal stack] |
             |----------------|

             |----------------|
   Display 0 | [Pinned stack] |
             | [Normal stack] | <- Moving task in here
Bottom       |----------------|

Bug: 113099160
Test: atest TaskStackContainersTests#testDisplayPositionWithPinnedStack
Change-Id: I877fd2acddeeb6d68fe6f4336dd202b9db11d94e