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/lexers/j/json.go

@@ -0,0 +1,55 @@
+package j
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// JSON lexer.
+var JSON = internal.Register(MustNewLexer(
+	&Config{
+		Name:         "JSON",
+		Aliases:      []string{"json"},
+		Filenames:    []string{"*.json"},
+		MimeTypes:    []string{"application/json"},
+		NotMultiline: true,
+		DotAll:       true,
+	},
+	Rules{
+		"whitespace": {
+			{`\s+`, Text, nil},
+		},
+		"simplevalue": {
+			{`(true|false|null)\b`, KeywordConstant, nil},
+			{`-?(0|[1-9]\d*)(\.\d+[eE](\+|-)?\d+|[eE](\+|-)?\d+|\.\d+)`, LiteralNumberFloat, nil},
+			{`-?(0|[1-9]\d*)`, LiteralNumberInteger, nil},
+			{`"(\\\\|\\"|[^"])*"`, LiteralStringDouble, nil},
+		},
+		"objectattribute": {
+			Include("value"),
+			{`:`, Punctuation, nil},
+			{`,`, Punctuation, Pop(1)},
+			{`\}`, Punctuation, Pop(2)},
+		},
+		"objectvalue": {
+			Include("whitespace"),
+			{`"(\\\\|\\"|[^"])*"`, NameTag, Push("objectattribute")},
+			{`\}`, Punctuation, Pop(1)},
+		},
+		"arrayvalue": {
+			Include("whitespace"),
+			Include("value"),
+			{`,`, Punctuation, nil},
+			{`\]`, Punctuation, Pop(1)},
+		},
+		"value": {
+			Include("whitespace"),
+			Include("simplevalue"),
+			{`\{`, Punctuation, Push("objectvalue")},
+			{`\[`, Punctuation, Push("arrayvalue")},
+		},
+		"root": {
+			Include("value"),
+		},
+	},
+))