Refactor diffFileInfo / DiffTreeStore (#24998)

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>