Synchronize stack position and size update for split screen

When entering split screen, the secondary window changes position so
it's below the primary split screen when minimized. The WSA at the same
time is also changing size to fit the area. However, the size doesn't
change until the client requests a new size and a frame with the correct
size comes in. This causes the stack to update position before the
resize which causes content to get cut off and then a jump when the resize
completes.

This change updates the WSA position as soon as it recognizes that the
stack changed position due to entering split screen secondary. The WSA
sets its position as the negative of the stack position, making the
calculated window position at (0,0). When a relayout is requested, the
WSA's position is requested back to (0,0), deferring until the new frame.
This will put the WSA position at (0,0) when a frame with the correct size
is drawn. This places the window position at the stack's new position in
the same transaction that a WSA frame with the new size is drawn.

Change-Id: I8c88d7784f827d66926fb5c382af2346028dc48f
Fixes: 74354855
Test: Entering split screen with quick step is smooth
Test: Entering split screen with old launcher still works