Re-activate the most recently-activated project search on cmd-shift-F

This commits adds the beginnings of an application state facility as a non-static place to store the most recently-activated search for each project.

I also store workspace items by descending order of their entity id so that we always fetch the newest item of a given type when calling `Workspace::item_of_type`.

crates/gpui/src/presenter.rs

@@ -281,6 +281,10 @@ impl<'a> UpgradeModelHandle for LayoutContext<'a> {
         self.app.upgrade_model_handle(handle)
     }
 
+    fn model_handle_is_upgradable<T: Entity>(&self, handle: &WeakModelHandle<T>) -> bool {
+        self.app.model_handle_is_upgradable(handle)
+    }
+
     fn upgrade_any_model_handle(&self, handle: &AnyWeakModelHandle) -> Option<AnyModelHandle> {
         self.app.upgrade_any_model_handle(handle)
     }