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/d/dart.go

@@ -0,0 +1,91 @@
+package d
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Dart lexer.
+var Dart = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Dart",
+		Aliases:   []string{"dart"},
+		Filenames: []string{"*.dart"},
+		MimeTypes: []string{"text/x-dart"},
+		DotAll:    true,
+	},
+	Rules{
+		"root": {
+			Include("string_literal"),
+			{`#!(.*?)$`, CommentPreproc, nil},
+			{`\b(import|export)\b`, Keyword, Push("import_decl")},
+			{`\b(library|source|part of|part)\b`, Keyword, nil},
+			{`[^\S\n]+`, Text, nil},
+			{`//.*?\n`, CommentSingle, nil},
+			{`/\*.*?\*/`, CommentMultiline, nil},
+			{`\b(class)\b(\s+)`, ByGroups(KeywordDeclaration, Text), Push("class")},
+			{`\b(assert|break|case|catch|continue|default|do|else|finally|for|if|in|is|new|return|super|switch|this|throw|try|while)\b`, Keyword, nil},
+			{`\b(abstract|async|await|const|extends|factory|final|get|implements|native|operator|set|static|sync|typedef|var|with|yield)\b`, KeywordDeclaration, nil},
+			{`\b(bool|double|dynamic|int|num|Object|String|void)\b`, KeywordType, nil},
+			{`\b(false|null|true)\b`, KeywordConstant, nil},
+			{`[~!%^&*+=|?:<>/-]|as\b`, Operator, nil},
+			{`[a-zA-Z_$]\w*:`, NameLabel, nil},
+			{`[a-zA-Z_$]\w*`, Name, nil},
+			{`[(){}\[\],.;]`, Punctuation, nil},
+			{`0[xX][0-9a-fA-F]+`, LiteralNumberHex, nil},
+			{`\d+(\.\d*)?([eE][+-]?\d+)?`, LiteralNumber, nil},
+			{`\.\d+([eE][+-]?\d+)?`, LiteralNumber, nil},
+			{`\n`, Text, nil},
+		},
+		"class": {
+			{`[a-zA-Z_$]\w*`, NameClass, Pop(1)},
+		},
+		"import_decl": {
+			Include("string_literal"),
+			{`\s+`, Text, nil},
+			{`\b(as|show|hide)\b`, Keyword, nil},
+			{`[a-zA-Z_$]\w*`, Name, nil},
+			{`\,`, Punctuation, nil},
+			{`\;`, Punctuation, Pop(1)},
+		},
+		"string_literal": {
+			{`r"""([\w\W]*?)"""`, LiteralStringDouble, nil},
+			{`r'''([\w\W]*?)'''`, LiteralStringSingle, nil},
+			{`r"(.*?)"`, LiteralStringDouble, nil},
+			{`r'(.*?)'`, LiteralStringSingle, nil},
+			{`"""`, LiteralStringDouble, Push("string_double_multiline")},
+			{`'''`, LiteralStringSingle, Push("string_single_multiline")},
+			{`"`, LiteralStringDouble, Push("string_double")},
+			{`'`, LiteralStringSingle, Push("string_single")},
+		},
+		"string_common": {
+			{`\\(x[0-9A-Fa-f]{2}|u[0-9A-Fa-f]{4}|u\{[0-9A-Fa-f]*\}|[a-z'\"$\\])`, LiteralStringEscape, nil},
+			{`(\$)([a-zA-Z_]\w*)`, ByGroups(LiteralStringInterpol, Name), nil},
+			{`(\$\{)(.*?)(\})`, ByGroups(LiteralStringInterpol, UsingSelf("root"), LiteralStringInterpol), nil},
+		},
+		"string_double": {
+			{`"`, LiteralStringDouble, Pop(1)},
+			{`[^"$\\\n]+`, LiteralStringDouble, nil},
+			Include("string_common"),
+			{`\$+`, LiteralStringDouble, nil},
+		},
+		"string_double_multiline": {
+			{`"""`, LiteralStringDouble, Pop(1)},
+			{`[^"$\\]+`, LiteralStringDouble, nil},
+			Include("string_common"),
+			{`(\$|\")+`, LiteralStringDouble, nil},
+		},
+		"string_single": {
+			{`'`, LiteralStringSingle, Pop(1)},
+			{`[^'$\\\n]+`, LiteralStringSingle, nil},
+			Include("string_common"),
+			{`\$+`, LiteralStringSingle, nil},
+		},
+		"string_single_multiline": {
+			{`'''`, LiteralStringSingle, Pop(1)},
+			{`[^\'$\\]+`, LiteralStringSingle, nil},
+			Include("string_common"),
+			{`(\$|\')+`, LiteralStringSingle, nil},
+		},
+	},
+))