Use git diff-tree for DiffFileTree on diff pages (#33514)

Modify Diff View FileTree to show all files

## Changes

* removes Show Status button on diff
* uses `git diff-tree` to generate the file tree for the diff
* doesn't reload the diff tree each time we load more files in the
preview
* selecting and unloaded file will keep loading until that file is
loaded
* removes `DiffFileList.vue` and "Show Stats" in diff options

## Open Questions

* selecting and unloaded file will keep loading until that file is
loaded. Is this behaviour okay? It matches what github does.

### Demo

In this demo I set `git.MAX_GIT_DIFF_FILES=1` in my `app.ini` to
demonstrate a worst case example. In most cases the behaviour isn't
nearly as jarring as we load a bunch of files at a time.


https://github.com/user-attachments/assets/72f29663-d6fc-472d-94fa-7fb5950c2836

---------

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

routers/web/repo/commit.go

@@ -344,18 +344,30 @@ func Diff(ctx *context.Context) {
 	ctx.Data["Reponame"] = repoName
 
 	var parentCommit *git.Commit
+	var parentCommitID string
 	if commit.ParentCount() > 0 {
 		parentCommit, err = gitRepo.GetCommit(parents[0])
 		if err != nil {
 			ctx.NotFound(err)
 			return
 		}
+		parentCommitID = parentCommit.ID.String()
 	}
 	setCompareContext(ctx, parentCommit, commit, userName, repoName)
 	ctx.Data["Title"] = commit.Summary() + " · " + base.ShortSha(commitID)
 	ctx.Data["Commit"] = commit
 	ctx.Data["Diff"] = diff
 
+	if !fileOnly {
+		diffTree, err := gitdiff.GetDiffTree(ctx, gitRepo, false, parentCommitID, commitID)
+		if err != nil {
+			ctx.ServerError("GetDiffTree", err)
+			return
+		}
+
+		ctx.PageData["DiffFiles"] = transformDiffTreeForUI(diffTree, nil)
+	}
+
 	statuses, _, err := git_model.GetLatestCommitStatus(ctx, ctx.Repo.Repository.ID, commitID, db.ListOptionsAll)
 	if err != nil {
 		log.Error("GetLatestCommitStatus: %v", err)