Use reactive store to share data between components (#23996)

Follow #23947

* Use reactive store to share data between components
* Remove no-op `this.hashListener = window.addEventListener()` because
`addEventListener` returns void/undefined.

Reference:


https://vuejs.org/guide/scaling-up/state-management.html#simple-state-management-with-reactivity-api


Screenshot (the same as before):

<details>

<img width="565" alt="image"
src="https://user-images.githubusercontent.com/2114189/230701282-bd61bfa3-7786-433b-9ad8-a88591112a02.png">


</details>

---------

Co-authored-by: silverwind <me@silverwind.io>

web_src/js/modules/stores.js

@@ -0,0 +1,5 @@
+import {reactive} from 'vue';
+
+export const DiffTreeStore = reactive({
+  selectedItem: '',
+});