Tiling: Maximised windows always display over non-maximized

[Koranir]

In the tiling window mode, maximized windows always display over non-maximized windows. This causes a few issues:

• It's impossible to access the non-maximized windows unless you unmaximize the maximized window (Alt+Tabbing can only switch between maximized windows).
• When switching into tiling mode with a maximized window in the background, it gets sent to the front.

A possible solution could be to treat the tiling windows as another "maximized layer", so you can switch between maximized and tiled windows easily. The tiling layer would also keep focus/be on the top when you switch to tiling mode if one of the contained windows has focus.

In addition, it would be nice to have a toggle that makes maximized windows unmaximize themselves when entering tiling mode - should be as easy as adding an if statement to https://github.com/pop-os/cosmic-comp/blob/536484e9dae289cc5590d35e18096ba24e7d0f1f/src/shell/workspace.rs#L878

Example of not being able to access windows until maximization is removed:

https://github.com/user-attachments/assets/534ce063-d9b4-4fe1-b237-650d7edb4d6e

[BrodieRobertson]

The same behavior occurs when clicking on an icon in the panel as well

[Drakulix]

Note, that this is by design atm, since maximized windows are supposed to be part of the floating layer and don't interact with tiled windows in that way. Allowing this would allow some tiled windows overlap the maximized window, which is not intended. (See also https://github.com/pop-os/cosmic-comp/issues/933)

However I do see the value of un-maximizing on toggling tiling mode. @pop-os/ux Any thoughts on this?