Purpose:
1. Make the whole code base have unified "item" layout
2. Clarify our "list" styles: "flex-relaxed-list", "flex-divided-list"
3. Prepare to replace legacy "ui relaxed list"
* https://github.com/go-gitea/gitea/pull/37445#discussion_r3144458865
4. Prepare for refactoring the "pull merge box", it needs the
"flex-divided-list"
* related to "Refactor pull request view (*)" like #37451
5. Fix legacy abuses of "flex-list", e.g.: repo home sidebar
/claim #35898Resolves#35898
### Summary of key changes:
1. Add file name search/Go to file functionality to repo button row.
2. Add backend functionality to delete directory
3. Add context menu for directories with functionality to copy path & delete a directory
4. Move Add/Upload file dropdown to right for parity with Github UI
5. Add tree view to the edit/upload UI
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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Resolve#29328
This pull request introduces a file tree on the left side when reviewing
files of a repository.
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Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>