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/g/genshi.go

@@ -0,0 +1,114 @@
+package g
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+	. "github.com/alecthomas/chroma/lexers/p"
+)
+
+// Genshi Text lexer.
+var GenshiText = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Genshi Text",
+		Aliases:   []string{"genshitext"},
+		Filenames: []string{},
+		MimeTypes: []string{"application/x-genshi-text", "text/x-genshi"},
+	},
+	Rules{
+		"root": {
+			{`[^#$\s]+`, Other, nil},
+			{`^(\s*)(##.*)$`, ByGroups(Text, Comment), nil},
+			{`^(\s*)(#)`, ByGroups(Text, CommentPreproc), Push("directive")},
+			Include("variable"),
+			{`[#$\s]`, Other, nil},
+		},
+		"directive": {
+			{`\n`, Text, Pop(1)},
+			{`(?:def|for|if)\s+.*`, Using(Python), Pop(1)},
+			{`(choose|when|with)([^\S\n]+)(.*)`, ByGroups(Keyword, Text, Using(Python)), Pop(1)},
+			{`(choose|otherwise)\b`, Keyword, Pop(1)},
+			{`(end\w*)([^\S\n]*)(.*)`, ByGroups(Keyword, Text, Comment), Pop(1)},
+		},
+		"variable": {
+			{`(?<!\$)(\$\{)(.+?)(\})`, ByGroups(CommentPreproc, Using(Python), CommentPreproc), nil},
+			{`(?<!\$)(\$)([a-zA-Z_][\w.]*)`, NameVariable, nil},
+		},
+	},
+))
+
+// Html+Genshi lexer.
+var GenshiHTMLTemplate = internal.Register(MustNewLexer(
+	&Config{
+		Name:         "Genshi HTML",
+		Aliases:      []string{"html+genshi", "html+kid"},
+		Filenames:    []string{},
+		MimeTypes:    []string{"text/html+genshi"},
+		NotMultiline: true,
+		DotAll:       true,
+	},
+	genshiMarkupRules,
+))
+
+// Genshi lexer.
+var Genshi = internal.Register(MustNewLexer(
+	&Config{
+		Name:         "Genshi",
+		Aliases:      []string{"genshi", "kid", "xml+genshi", "xml+kid"},
+		Filenames:    []string{"*.kid"},
+		MimeTypes:    []string{"application/x-genshi", "application/x-kid"},
+		NotMultiline: true,
+		DotAll:       true,
+	},
+	genshiMarkupRules,
+))
+
+var genshiMarkupRules = Rules{
+	"root": {
+		{`[^<$]+`, Other, nil},
+		{`(<\?python)(.*?)(\?>)`, ByGroups(CommentPreproc, Using(Python), CommentPreproc), nil},
+		{`<\s*(script|style)\s*.*?>.*?<\s*/\1\s*>`, Other, nil},
+		{`<\s*py:[a-zA-Z0-9]+`, NameTag, Push("pytag")},
+		{`<\s*[a-zA-Z0-9:.]+`, NameTag, Push("tag")},
+		Include("variable"),
+		{`[<$]`, Other, nil},
+	},
+	"pytag": {
+		{`\s+`, Text, nil},
+		{`[\w:-]+\s*=`, NameAttribute, Push("pyattr")},
+		{`/?\s*>`, NameTag, Pop(1)},
+	},
+	"pyattr": {
+		{`(")(.*?)(")`, ByGroups(LiteralString, Using(Python), LiteralString), Pop(1)},
+		{`(')(.*?)(')`, ByGroups(LiteralString, Using(Python), LiteralString), Pop(1)},
+		{`[^\s>]+`, LiteralString, Pop(1)},
+	},
+	"tag": {
+		{`\s+`, Text, nil},
+		{`py:[\w-]+\s*=`, NameAttribute, Push("pyattr")},
+		{`[\w:-]+\s*=`, NameAttribute, Push("attr")},
+		{`/?\s*>`, NameTag, Pop(1)},
+	},
+	"attr": {
+		{`"`, LiteralString, Push("attr-dstring")},
+		{`'`, LiteralString, Push("attr-sstring")},
+		{`[^\s>]*`, LiteralString, Pop(1)},
+	},
+	"attr-dstring": {
+		{`"`, LiteralString, Pop(1)},
+		Include("strings"),
+		{`'`, LiteralString, nil},
+	},
+	"attr-sstring": {
+		{`'`, LiteralString, Pop(1)},
+		Include("strings"),
+		{`'`, LiteralString, nil},
+	},
+	"strings": {
+		{`[^"'$]+`, LiteralString, nil},
+		Include("variable"),
+	},
+	"variable": {
+		{`(?<!\$)(\$\{)(.+?)(\})`, ByGroups(CommentPreproc, Using(Python), CommentPreproc), nil},
+		{`(?<!\$)(\$)([a-zA-Z_][\w\.]*)`, NameVariable, nil},
+	},
+}