Report re-sized stacks/task as fullscreen when docked stack isn't visible

When a docked stack exist we resize all other stacks and crop their
window content to the stack size. This was also been done when the
docked stack exist, but not visible. E.g the primary user has a docked
stack, but the secondary user doesn't, so the windows of the secondary
user get cropped.
We now report stacks/task sizes as fullscreen whenever the docked stack
isn't visible.

Bug: 24366804
Change-Id: Ia3f24e6f7d33fc175348e27db24a15ce3027e6f7