Fixes wrong cursor icons and sizes on KDE 6 (and possibly other
compositors)

Gnome still doesn't support this protocol, so to fix cursor settings
there we'll need to read `gsettings`.

Before:

![image](https://github.com/zed-industries/zed/assets/71973804/f0c3dc1b-2bed-43f7-b579-df6c9c0b547f)

After:

![image](https://github.com/zed-industries/zed/assets/71973804/6de639f9-653d-4896-80ca-b7c69641eded)


Release Notes:

- N/A