Follow #22719
### Major changes
1. `ServerError` doesn't do format, so remove the `%s`
2. Simplify `RenderBranchFeed` (slightly)
3. Remove unused `BranchFeedRSS`
4. Make `feed.RenderBranchFeed` respect `EnableFeed` config
5. Make `RepoBranchTagSelector.vue` respect `EnableFeed` setting,
otherwise there is always RSS icon
6. The `(branchURLPrefix + item.url).replace('src', 'rss')` doesn't seem
right for all cases, for example, the string `src` could appear in
`branchURLPrefix`, so we need a separate `rssURLPrefix`
7. The `<a>` in Vue menu needs `@click.stop`, otherwise the menu itself
would be triggered at the same time
8. Change `<a><button></button></a>` to `<a role=button>`
9. Use `{{PathEscapeSegments .TreePath}}` instead of `{{range $i, $v :=
.TreeNames}}/{{$v}}{{end}}`
Screenshot of changed parts:
<details>
</details>
### Other thoughts
Should we remove the RSS icon from the branch dropdown list? It seems
too complex for a list UI, and users already have the chance to get the
RSS feed URL from "branches" page.
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Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: silverwind <me@silverwind.io>
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