[feature request] Add option for scrolling window management

[Lillian-Violet]

While the tiling window management style is tried and tested, and quite good for a lot of use cases. I would like to see an option for scrolling window management like the cardboard wm POC. I have seen a lot of enthousiasm for this concept, and I think a lot of people would adopt it given the chance. But it hasn't really been implemented in a big project in a satisfactory way.

The main concepts are:

1. Basics are like a normal tile window manager; you have windows that open to a snapped grid, you can resize and reposition the windows.
2. Instead of new windows resizing old windows to fit on the screen, they open to the side off-screen.
3. You can change what application you are looking at by scrolling through your tiles (with three fingers on a touchpad, holding specific keys etc.) to change what applications are in the center of your screen.

[Drakulix]

We will probably not introduce more window management concepts at this point in development.

But there have been frequent requests for more options, so we might (long-term) try to provide an api to have external programs add new window management options. Additionally we want to enable changing the compositor, so you could e.g. run niri instead of cosmic-comp in your session to get scrolling window management.