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/r/reasonml.go

@@ -0,0 +1,67 @@
+package r
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Reasonml lexer.
+var Reasonml = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "ReasonML",
+		Aliases:   []string{"reason", "reasonml"},
+		Filenames: []string{"*.re", "*.rei"},
+		MimeTypes: []string{"text/x-reasonml"},
+	},
+	Rules{
+		"escape-sequence": {
+			{`\\[\\"\'ntbr]`, LiteralStringEscape, nil},
+			{`\\[0-9]{3}`, LiteralStringEscape, nil},
+			{`\\x[0-9a-fA-F]{2}`, LiteralStringEscape, nil},
+		},
+		"root": {
+			{`\s+`, Text, nil},
+			{`false|true|\(\)|\[\]`, NameBuiltinPseudo, nil},
+			{`\b([A-Z][\w\']*)(?=\s*\.)`, NameNamespace, Push("dotted")},
+			{`\b([A-Z][\w\']*)`, NameClass, nil},
+			{`//.*?\n`, CommentSingle, nil},
+			{`\/\*(?![\/])`, CommentMultiline, Push("comment")},
+			{`\b(as|assert|begin|class|constraint|do|done|downto|else|end|exception|external|false|for|fun|esfun|function|functor|if|in|include|inherit|initializer|lazy|let|switch|module|pub|mutable|new|nonrec|object|of|open|pri|rec|sig|struct|then|to|true|try|type|val|virtual|when|while|with)\b`, Keyword, nil},
+			{"(~|\\}|\\|]|\\||\\|\\||\\{<|\\{|`|_|]|\\[\\||\\[>|\\[<|\\[|\\?\\?|\\?|>\\}|>]|>|=|<-|<|;;|;|:>|:=|::|:|\\.\\.\\.|\\.\\.|\\.|=>|-\\.|-|,|\\+|\\*|\\)|\\(|&&|&|#|!=)", OperatorWord, nil},
+			{`([=<>@^|&+\*/$%-]|[!?~])?[!$%&*+\./:<=>?@^|~-]`, Operator, nil},
+			{`\b(and|asr|land|lor|lsl|lsr|lxor|mod|or)\b`, OperatorWord, nil},
+			{`\b(unit|int|float|bool|string|char|list|array)\b`, KeywordType, nil},
+			{`[^\W\d][\w']*`, Name, nil},
+			{`-?\d[\d_]*(.[\d_]*)?([eE][+\-]?\d[\d_]*)`, LiteralNumberFloat, nil},
+			{`0[xX][\da-fA-F][\da-fA-F_]*`, LiteralNumberHex, nil},
+			{`0[oO][0-7][0-7_]*`, LiteralNumberOct, nil},
+			{`0[bB][01][01_]*`, LiteralNumberBin, nil},
+			{`\d[\d_]*`, LiteralNumberInteger, nil},
+			{`'(?:(\\[\\\"'ntbr ])|(\\[0-9]{3})|(\\x[0-9a-fA-F]{2}))'`, LiteralStringChar, nil},
+			{`'.'`, LiteralStringChar, nil},
+			{`'`, Keyword, nil},
+			{`"`, LiteralStringDouble, Push("string")},
+			{`[~?][a-z][\w\']*:`, NameVariable, nil},
+		},
+		"comment": {
+			{`[^\/*]+`, CommentMultiline, nil},
+			{`\/\*`, CommentMultiline, Push()},
+			{`\*\/`, CommentMultiline, Pop(1)},
+			{`[\*]`, CommentMultiline, nil},
+		},
+		"string": {
+			{`[^\\"]+`, LiteralStringDouble, nil},
+			Include("escape-sequence"),
+			{`\\\n`, LiteralStringDouble, nil},
+			{`"`, LiteralStringDouble, Pop(1)},
+		},
+		"dotted": {
+			{`\s+`, Text, nil},
+			{`\.`, Punctuation, nil},
+			{`[A-Z][\w\']*(?=\s*\.)`, NameNamespace, nil},
+			{`[A-Z][\w\']*`, NameClass, Pop(1)},
+			{`[a-z_][\w\']*`, Name, Pop(1)},
+			Default(Pop(1)),
+		},
+	},
+))