Add cosmic-workspace-v2, image source, toplevel info changes

This new protocol extends `ext-workspace-v1` with the same additional
functionality `cosmic-workspace-v1` provided. Toplevel info and toplevel
management are also updated to use ext handles, and there's an image
source for ext workspaces.

For now, the old protocol is still supported.

src/wayland/protocols/workspace/ext.rs

@@ -392,6 +392,7 @@ where
             }
         }
     };
+    let instance = instance.clone();
 
     let mut handle_state = instance.data::<WorkspaceData>().unwrap().lock().unwrap();
     let mut changed = false;
@@ -442,5 +443,13 @@ where
     }
     // TODO ext_workspace_handle_v1::id
 
+    if let Some(cosmic_v2_handle) = handle_state
+        .cosmic_v2_handle
+        .as_ref()
+        .and_then(|x| x.upgrade().ok())
+    {
+        changed |= super::cosmic_v2::send_workspace_to_client(&cosmic_v2_handle, workspace);
+    }
+
     changed
 }