Sets the workspace on which applications will be launched.
This only works when running under a window manager that supports multiple workspaces, as described in the Extended Window Manager Hints. Specifically this sets the `_NET_WM_DESKTOP` property described in that spec.
This only works when using the X11 backend.
When the workspace is not specified or desktop is set to -1, it is up to the window manager to pick one, typically it will
be the current workspace.
| this |
a `GdkAppLaunchContext` |
| desktop |
the number of a workspace, or -1 |