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/t/twig.go

@@ -0,0 +1,54 @@
+package t
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Twig lexer.
+var Twig = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Twig",
+		Aliases:   []string{"twig"},
+		Filenames: []string{},
+		MimeTypes: []string{"application/x-twig"},
+		DotAll:    true,
+	},
+	Rules{
+		"root": {
+			{`[^{]+`, Other, nil},
+			{`\{\{`, CommentPreproc, Push("var")},
+			{`\{\#.*?\#\}`, Comment, nil},
+			{`(\{%)(-?\s*)(raw)(\s*-?)(%\})(.*?)(\{%)(-?\s*)(endraw)(\s*-?)(%\})`, ByGroups(CommentPreproc, Text, Keyword, Text, CommentPreproc, Other, CommentPreproc, Text, Keyword, Text, CommentPreproc), nil},
+			{`(\{%)(-?\s*)(verbatim)(\s*-?)(%\})(.*?)(\{%)(-?\s*)(endverbatim)(\s*-?)(%\})`, ByGroups(CommentPreproc, Text, Keyword, Text, CommentPreproc, Other, CommentPreproc, Text, Keyword, Text, CommentPreproc), nil},
+			{`(\{%)(-?\s*)(filter)(\s+)((?:[\\_a-z]|[^\x00-\x7f])(?:[\\\w-]|[^\x00-\x7f])*)`, ByGroups(CommentPreproc, Text, Keyword, Text, NameFunction), Push("tag")},
+			{`(\{%)(-?\s*)([a-zA-Z_]\w*)`, ByGroups(CommentPreproc, Text, Keyword), Push("tag")},
+			{`\{`, Other, nil},
+		},
+		"varnames": {
+			{`(\|)(\s*)((?:[\\_a-z]|[^\x00-\x7f])(?:[\\\w-]|[^\x00-\x7f])*)`, ByGroups(Operator, Text, NameFunction), nil},
+			{`(is)(\s+)(not)?(\s*)((?:[\\_a-z]|[^\x00-\x7f])(?:[\\\w-]|[^\x00-\x7f])*)`, ByGroups(Keyword, Text, Keyword, Text, NameFunction), nil},
+			{`(?i)(true|false|none|null)\b`, KeywordPseudo, nil},
+			{`(in|not|and|b-and|or|b-or|b-xor|isif|elseif|else|importconstant|defined|divisibleby|empty|even|iterable|odd|sameasmatches|starts\s+with|ends\s+with)\b`, Keyword, nil},
+			{`(loop|block|parent)\b`, NameBuiltin, nil},
+			{`(?:[\\_a-z]|[^\x00-\x7f])(?:[\\\w-]|[^\x00-\x7f])*`, NameVariable, nil},
+			{`\.(?:[\\_a-z]|[^\x00-\x7f])(?:[\\\w-]|[^\x00-\x7f])*`, NameVariable, nil},
+			{`\.[0-9]+`, LiteralNumber, nil},
+			{`:?"(\\\\|\\"|[^"])*"`, LiteralStringDouble, nil},
+			{`:?'(\\\\|\\'|[^'])*'`, LiteralStringSingle, nil},
+			{`([{}()\[\]+\-*/,:~%]|\.\.|\?|:|\*\*|\/\/|!=|[><=]=?)`, Operator, nil},
+			{`[0-9](\.[0-9]*)?(eE[+-][0-9])?[flFLdD]?|0[xX][0-9a-fA-F]+[Ll]?`, LiteralNumber, nil},
+		},
+		"var": {
+			{`\s+`, Text, nil},
+			{`(-?)(\}\})`, ByGroups(Text, CommentPreproc), Pop(1)},
+			Include("varnames"),
+		},
+		"tag": {
+			{`\s+`, Text, nil},
+			{`(-?)(%\})`, ByGroups(Text, CommentPreproc), Pop(1)},
+			Include("varnames"),
+			{`.`, Punctuation, nil},
+		},
+	},
+))