Entirely unnecessary for the current version of `cycleWindowSets`, but
if anyone ever wants to use `greedyView`, this shows that it's not at
all complicated to adapt `unView` to that.
To make this more "obviously correct", make it resemble the `view`
implementation, just do the exact reverse. Now the only complex bit is
the "undelete" operation.
This also fixes another issue: state was only preserved in the focused
workspace, but it may have changed in another visible workspace as well.
The property test is updated to test this.
