Improve wiki sidebar and TOC (#25460) (#25477)
Backport #25460 by @wxiaoguang
Close #20976
Close #20975
1. Fix the bug: the TOC in footer was incorrectly rendered as main
content's TOC
2. Fix the layout: on mobile, the TOC is put above the main content,
while the sidebar is put below the main content
3. Auto collapse the TOC on mobile
ps: many styles of "wiki.css" are moved from old css files, so leave
nits to following PRs.
### for desktop
### for mobile
### other changed pages
<details>
</details>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Giteabot