Per-window fullscreen/maximization state

[Vladimir-csp]

Copy of #9528

Currently fullscreen/maximization is effectively a workspace-level state. Switching away from a fullscreened window makes the next window fullscreen.

Feature idea: per-window fullscreen/maximization state:

• When switching away from a fullscreened/maximized window to a tiled window, it shrinks back to its tile, scaled, without state update to the client, maybe with some overlayed icon, like view-fullscreen or window_fullscreen.
• When switching back, it goes back to its state like nothing happened.
• If switching to a floating window, do nothing, just bring that floating window forward.
• Click on the shrunk fullscreen window tile restores it and is consumed.

[Ferk]

without state update to the client

This is an important bit, imho.

Even for the current case of workspace-level fullscreen mode, the fact that the clients are under-the-hood being told they were resized adds way too much noise as the clients re-organize themselves and you can often visually see how their contents resize, adding delay to the operation of switching windows.

So I feel fullscreen windows should always in general behave in the way you described (ie. remain in a "fullscreen" shrinked mode when not active) even for the workspace-level, the only difference being that in that mode all windows in the workspace would be fullscreen, whereas in your example only 1 window would.