applets/showdesktop: limit Minimize All by desktop/activity
The Minimize All widget currently minimizes all windows on all virtual desktops, which is likely not what the user intended. The same, perhaps even more counterintuitively, is true for activities.
This change limits minimization to the current virtual desktop and/or activity.
This is a change in default behavior with no configuration option. I think it's enough to do the right thing and not clutter up the UI with irrelevant options; see also comment 1 in BUG: 475507. If desired, I can make the behavior optional.
I have changed this so that the widget now tracks the active state and the lists of windows that it minimized (if any) separately per activity/desktop combination. A user can now press Minimize All, do all sorts of other things on other activities/desktops, come back to the original desktop in the original activity, press the button again and have their windows restored. I think this is a significant QoL upgrade over the existing version, where restoring will not work if the user activated any window, even if it was on another activity or desktop.
BUG: 475507 FIXED-IN: 6.2.0