Take slice instead of array in set_workspace_coordinates

As far as I can tell this is equivalent, and there's no particular
reason to use an array. Arrays of options for variable-length arrays are
awkward.

src/shell/mod.rs

@@ -4023,7 +4023,7 @@ fn workspace_set_idx(
     handle: &WorkspaceHandle,
 ) {
     state.set_workspace_name(handle, format!("{}", idx));
-    state.set_workspace_coordinates(handle, [Some(idx as u32), Some(output_pos as u32), None]);
+    state.set_workspace_coordinates(handle, &[idx as u32, output_pos as u32]);
 }
 
 pub fn check_grab_preconditions(

src/wayland/protocols/workspace/mod.rs

@@ -669,22 +669,14 @@ where
         self.0.workspace_coordinates(workspace)
     }
 
-    pub fn set_workspace_coordinates(
-        &mut self,
-        workspace: &WorkspaceHandle,
-        coords: [Option<u32>; 3],
-    ) {
+    pub fn set_workspace_coordinates(&mut self, workspace: &WorkspaceHandle, coords: &[u32]) {
         if let Some(workspace) = self
             .0
             .groups
             .iter_mut()
             .find_map(|g| g.workspaces.iter_mut().find(|w| w.id == workspace.id))
         {
-            workspace.coordinates = coords
-                .iter()
-                .flat_map(std::convert::identity)
-                .copied()
-                .collect();
+            workspace.coordinates = coords.to_vec();
         }
     }