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/groovy.go

@@ -0,0 +1,58 @@
+package g
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Groovy lexer.
+var Groovy = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Groovy",
+		Aliases:   []string{"groovy"},
+		Filenames: []string{"*.groovy", "*.gradle"},
+		MimeTypes: []string{"text/x-groovy"},
+		DotAll:    true,
+	},
+	Rules{
+		"root": {
+			{`#!(.*?)$`, CommentPreproc, Push("base")},
+			Default(Push("base")),
+		},
+		"base": {
+			{`^(\s*(?:[a-zA-Z_][\w.\[\]]*\s+)+?)([a-zA-Z_]\w*)(\s*)(\()`, ByGroups(UsingSelf("root"), NameFunction, Text, Operator), nil},
+			{`[^\S\n]+`, Text, nil},
+			{`//.*?\n`, CommentSingle, nil},
+			{`/\*.*?\*/`, CommentMultiline, nil},
+			{`@[a-zA-Z_][\w.]*`, NameDecorator, nil},
+			{`(as|assert|break|case|catch|continue|default|do|else|finally|for|if|in|goto|instanceof|new|return|switch|this|throw|try|while|in|as)\b`, Keyword, nil},
+			{`(abstract|const|enum|extends|final|implements|native|private|protected|public|static|strictfp|super|synchronized|throws|transient|volatile)\b`, KeywordDeclaration, nil},
+			{`(def|boolean|byte|char|double|float|int|long|short|void)\b`, KeywordType, nil},
+			{`(package)(\s+)`, ByGroups(KeywordNamespace, Text), nil},
+			{`(true|false|null)\b`, KeywordConstant, nil},
+			{`(class|interface)(\s+)`, ByGroups(KeywordDeclaration, Text), Push("class")},
+			{`(import)(\s+)`, ByGroups(KeywordNamespace, Text), Push("import")},
+			{`""".*?"""`, LiteralStringDouble, nil},
+			{`'''.*?'''`, LiteralStringSingle, nil},
+			{`"(\\\\|\\"|[^"])*"`, LiteralStringDouble, nil},
+			{`'(\\\\|\\'|[^'])*'`, LiteralStringSingle, nil},
+			{`\$/((?!/\$).)*/\$`, LiteralString, nil},
+			{`/(\\\\|\\"|[^/])*/`, LiteralString, nil},
+			{`'\\.'|'[^\\]'|'\\u[0-9a-fA-F]{4}'`, LiteralStringChar, nil},
+			{`(\.)([a-zA-Z_]\w*)`, ByGroups(Operator, NameAttribute), nil},
+			{`[a-zA-Z_]\w*:`, NameLabel, nil},
+			{`[a-zA-Z_$]\w*`, Name, nil},
+			{`[~^*!%&\[\](){}<>|+=:;,./?-]`, Operator, nil},
+			{`[0-9][0-9]*\.[0-9]+([eE][0-9]+)?[fd]?`, LiteralNumberFloat, nil},
+			{`0x[0-9a-fA-F]+`, LiteralNumberHex, nil},
+			{`[0-9]+L?`, LiteralNumberInteger, nil},
+			{`\n`, Text, nil},
+		},
+		"class": {
+			{`[a-zA-Z_]\w*`, NameClass, Pop(1)},
+		},
+		"import": {
+			{`[\w.]+\*?`, NameNamespace, Pop(1)},
+		},
+	},
+))