Break out helper functions from the frontend's managers and stores (#3920)

* Move destructor call to each manager/store constructor for safety

* Break out utility functions

frontend/src/stores/fullscreen.ts

@@ -22,6 +22,8 @@ if (import.meta.hot) import.meta.hot.data.store = store;
 const { subscribe, update } = store;
 
 export function createFullscreenStore(editor: Editor) {
+	destroyFullscreenStore();
+
 	editorRef = editor;
 
 	editor.subscriptions.subscribeFrontendMessage("WindowFullscreen", () => {