workspace: Clip to allocation when not in window picker state

We want to avoid windows that are overlapping the monitor edges from overflowing the small workspace strip when showing the app grid. To do that, enable clip_to_allocation on the Workspace actor when our stateAdjustment value is 0. The reason we can't use "stateAdjustement !== 1" here is that the app icons we show above the previews overflow the allocation, and those would get clipped while they're animating in/out.

Fixes #3716 (closed)