fix(editor): Fix local storage flags defaulting to undefined string (#7603)

useStorage takes the default value `undefined` and sets it in local
storage.. also returns "undefined" as string which breaks onboarding
flows

Github issue / Community forum post (link here to close automatically):

packages/editor-ui/src/composables/useStorage.ts

@@ -0,0 +1,13 @@
+import { useStorage as useStorageComposable } from '@vueuse/core';
+import type { Ref } from 'vue';
+
+export function useStorage(key: string): Ref<string | null> {
+	const data = useStorageComposable(key, null, undefined, { writeDefaults: false });
+
+	// bug in 1.15.1
+	if (data.value === 'undefined') {
+		data.value = null;
+	}
+
+	return data;
+}