Thanks to @yuin

fix #12376

* Server-side syntax hilighting for all code

This PR does a few things:

* Remove all traces of highlight.js
* Use chroma library to provide fast syntax hilighting directly on the server
* Provide syntax hilighting for diffs
* Re-style both unified and split diffs views
* Add custom syntax hilighting styling for both regular and arc-green

Fixes #7729
Fixes #10157
Fixes #11825
Fixes #7728
Fixes #3872
Fixes #3682

And perhaps gets closer to #9553

* fix line marker

* fix repo search

* Fix single line select

* properly load settings

* npm uninstall highlight.js

* review suggestion

* code review

* forgot to call function

* fix test

* Apply suggestions from code review

suggestions from @silverwind thanks

Co-authored-by: silverwind <me@silverwind.io>

* code review

* copy/paste error

* Use const for highlight size limit

* Update web_src/less/_repository.less

Co-authored-by: Lauris BH <lauris@nix.lv>

* update size limit to 1MB and other styling tweaks

* fix highlighting for certain diff sections

* fix test

* add worker back as suggested

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lauris BH <lauris@nix.lv>

Add goldmark-meta to render yaml frontmatter as a table

Fix #5377

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Fix task-list checkbox styling

The pandoc renderer will append the class "task-list" to the ul element
wrapping a li with one or more check-boxes. This allows us to select for
them, removing their list-style-type property. However, goldmark and the
gfm spec doesn't specify the "task-list" class name, so we can't use
that to fix the issue there.

Signed-off-by: Alexander Scheel <alexander.m.scheel@gmail.com>

* Update to goldmark v1.1.25

This version adds the missing space after a checkbox.

Resolves: #9656

Signed-off-by: Alexander Scheel <alexander.m.scheel@gmail.com>

Co-authored-by: zeripath <art27@cantab.net>

vendor update

* Move to goldmark

Markdown rendering moved from blackfriday to the goldmark.

Multiple subtle changes required to the goldmark extensions to keep
current rendering and defaults.

Can go further with goldmark linkify and have this work within markdown
rendering making the link processor unnecessary.

Need to think about how to go about allowing extensions - at present it
seems that these would be hard to do without recompilation.

* linter fixes

Co-authored-by: Lauris BH <lauris@nix.lv>