Server-side syntax highlighting for all code (#12047)

* 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>

vendor/github.com/alecthomas/chroma/.goreleaser.yml

@@ -0,0 +1,33 @@
+project_name: chroma
+release:
+  github:
+    owner: alecthomas
+    name: chroma
+brews:
+  -
+    install: bin.install "chroma"
+builds:
+- goos:
+    - linux
+    - darwin
+    - windows
+  goarch:
+    - amd64
+    - "386"
+  goarm:
+    - "6"
+  main: ./cmd/chroma/main.go
+  ldflags: -s -w -X main.version={{.Version}} -X main.commit={{.Commit}} -X main.date={{.Date}}
+  binary: chroma
+archives:
+  -
+    format: tar.gz
+    name_template: '{{ .Binary }}-{{ .Version }}-{{ .Os }}-{{ .Arch }}{{ if .Arm }}v{{
+    .Arm }}{{ end }}'
+    files:
+      - COPYING
+      - README*
+snapshot:
+  name_template: SNAPSHOT-{{ .Commit }}
+checksum:
+  name_template: '{{ .ProjectName }}-{{ .Version }}-checksums.txt'