Backport #28454 (the only conflict is caused by some comments)
* Close #24483
* Close #28123
* Close #23682
* Close #23149
(cherry picked from commit a3f403f438)
Conflicts:
modules/setting/ui.go
trivial context conflict
Change all license headers to comply with REUSE specification.
Fix #16132
Co-authored-by: flynnnnnnnnnn <flynnnnnnnnnn@github>
Co-authored-by: John Olheiser <john.olheiser@gmail.com>
Use Unicode placeholders to replace HTML tags and HTML entities first, then do diff, then recover the HTML tags and HTML entities. Now the code diff with highlight has stable behavior, and won't emit broken tags.