fix https://github.com/go-gitea/gitea/issues/32226
in https://github.com/go-gitea/gitea/pull/27775 , it do some changes to
only show diff file tree when more than one file changed. But looks it
also break the `diff-file-list` logic, which looks not expected change.
so try fix it.
/cc @silverwind
example view:

Signed-off-by: a1012112796 <1012112796@qq.com>
(cherry picked from commit c4b2808b896dd86323c6a0d119c8cf24752d4d8a)
Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>
Conflicts:
- web_src/js/features/repo-diff-filetree.js
web_src/js/features/repo-diff.js
Conflicts resolved by manually applying the changes.
- Replace all default exports with named exports, except for Vue SFCs
- Remove names from Vue SFCs, they are automatically inferred from the
filename
- Misc whitespace-related tweaks
This PR adds a filetree to the left side of the files/diff view.
Initially the filetree will not be shown and may be shown via a new
"Show file tree" button.
Showing and hiding is using the same icon as github. Folders are
collapsible. On small devices (max-width 991 PX) the file tree will be
hidden.
Close#18192
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>