Refactor diffFileInfo / DiffTreeStore (#24998)

Follow  #21012, #22399

Replace #24983, fix #24938

Help #24956

Now, the `window.config.pageData.diffFileInfo` itself is a reactive
store, so it's quite easy to sync values/states by it, no need to do
"doLoadMoreFiles" or "callback".

Screenshot: these two buttons both work. After complete loading, the UI
is also right.

<details>


![image](https://github.com/go-gitea/gitea/assets/2114189/cc6310fd-7f27-45ea-ab4f-24952a87b421)


![image](https://github.com/go-gitea/gitea/assets/2114189/4c11dd67-ac03-4568-8541-91204d27a4e3)


![image](https://github.com/go-gitea/gitea/assets/2114189/38a22cec-41be-41e6-a209-f347b7a4c1de)

</details>

1 files changed, 8 insertions, 3 deletions

diff --git a/web_src/js/modules/stores.js b/web_src/js/modules/stores.js
index 24b913ce11..1a0ed7eda1 100644
--- a/web_src/js/modules/stores.js
+++ b/web_src/js/modules/stores.js
@@ -1,5 +1,10 @@
 import {reactive} from 'vue';
 
-export const DiffTreeStore = reactive({
-  selectedItem: '',
-});
+let diffTreeStoreReactive;
+export function diffTreeStore() {
+  if (!diffTreeStoreReactive) {
+    diffTreeStoreReactive = reactive(window.config.pageData.diffFileInfo);
+    window.config.pageData.diffFileInfo = diffTreeStoreReactive;
+  }
+  return diffTreeStoreReactive;
+}