fix: keyboard shortcuts for left/right workspaces

[laikq]

Add keyboard shortcuts for left/right workspace switching & window moving.

• SUPER + Ctrl + left/right for workspace switching
• SUPER + Ctrl + Shift + left/right for moving windows between workspaces

Fix #1776

Hopefully useful for some people installing pop-shell on vanilla gnome.

[jacobgkau]

Because this script isn't part of the actual extension source code or package, this won't affect typical Pop!_OS 22.04 usage with the packaged version of pop-shell. It will only affect manual installations on other distros, or on Pop!_OS for the purpose of development.

On Debian 12 with GNOME 43, I confirmed this makes the Ctrl-Super-Left/Right shortcuts switch horizontal workspaces as expected.

On Pop!_OS 22.04, the Ctrl-Super-Left/Right shortcuts snap a window to the left or right side of the screen by default. I installed the packaged version of this to double-check that no changes were observed. I then installed using make local-install to have the script applied to the system; after that, the Ctrl-Super-Left/Right shortcuts didn't do anything, because they'd been assigned to switch horizontal workspaces, but Pop!_OS 22.04 doesn't use horizontal workspaces.

With that in mind, I don't think this should be merged as-is, since it breaks one of the expected shortcuts on a Pop!_OS system. On Debian, the left/right snap shortcut is just Super-Left/Right by default, which Pop!_Shell obviously already overrides with its shortcuts to move focus to the left/right, which is why this regression wouldn't be noticed on Debian.

There are a couple of paths forward for this PR:

• Apply instead to master_noble. Although this won't help with Debian 12 since it uses GNOME 43, this extension is no longer being used in Pop!_OS 24.04 (Noble), nor is the vertical workspaces extension; that means Pop!_OS's vertical workspaces are no longer a concern, nor is breaking Pop!_OS compatibility. The change could be made on that branch to benefit future users on later versions of GNOME.
• A check could be made either for the OS (don't apply the left/right workspace shortcuts on Pop!_OS) or for the existing shortcuts (don't apply the left/right workspace shortcuts if those shortcuts are assigned to snap windows) in the configure script.

[jacobgkau]

If we did want to apply this to master_noble, we'd want to give some thought to whether a different pair of shortcuts could take on the role of snapping windows to the left/right. Although I agree navigating workspaces is probably more useful than snapping as a keyboard shortcut (especially since snapping happens outside of the tiling workflow), snapping has long been part of the Pop!_Shell regression testing checklist and is thus a feature we intended to support with the Pop!_Shell experience. (The simplest solution would be swapping it to Ctrl-Super-Up/Down since those wouldn't be in use with horizontal workspaces, but there'd be no intuitive answer to whether Up should snap left or right, and vice versa.)