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/l/lua.go

@@ -0,0 +1,75 @@
+package l
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Lua lexer.
+var Lua = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Lua",
+		Aliases:   []string{"lua"},
+		Filenames: []string{"*.lua", "*.wlua"},
+		MimeTypes: []string{"text/x-lua", "application/x-lua"},
+	},
+	Rules{
+		"root": {
+			{`#!.*`, CommentPreproc, nil},
+			Default(Push("base")),
+		},
+		"ws": {
+			{`(?:--\[(=*)\[[\w\W]*?\](\1)\])`, CommentMultiline, nil},
+			{`(?:--.*$)`, CommentSingle, nil},
+			{`(?:\s+)`, Text, nil},
+		},
+		"base": {
+			Include("ws"),
+			{`(?i)0x[\da-f]*(\.[\da-f]*)?(p[+-]?\d+)?`, LiteralNumberHex, nil},
+			{`(?i)(\d*\.\d+|\d+\.\d*)(e[+-]?\d+)?`, LiteralNumberFloat, nil},
+			{`(?i)\d+e[+-]?\d+`, LiteralNumberFloat, nil},
+			{`\d+`, LiteralNumberInteger, nil},
+			{`(?s)\[(=*)\[.*?\]\1\]`, LiteralString, nil},
+			{`::`, Punctuation, Push("label")},
+			{`\.{3}`, Punctuation, nil},
+			{`[=<>|~&+\-*/%#^]+|\.\.`, Operator, nil},
+			{`[\[\]{}().,:;]`, Punctuation, nil},
+			{`(and|or|not)\b`, OperatorWord, nil},
+			{`(break|do|else|elseif|end|for|if|in|repeat|return|then|until|while)\b`, KeywordReserved, nil},
+			{`goto\b`, KeywordReserved, Push("goto")},
+			{`(local)\b`, KeywordDeclaration, nil},
+			{`(true|false|nil)\b`, KeywordConstant, nil},
+			{`(function)\b`, KeywordReserved, Push("funcname")},
+			{`[A-Za-z_]\w*(\.[A-Za-z_]\w*)?`, Name, nil},
+			{`'`, LiteralStringSingle, Combined("stringescape", "sqs")},
+			{`"`, LiteralStringDouble, Combined("stringescape", "dqs")},
+		},
+		"funcname": {
+			Include("ws"),
+			{`[.:]`, Punctuation, nil},
+			{`(?:[^\W\d]\w*)(?=(?:(?:--\[(=*)\[[\w\W]*?\](\2)\])|(?:--.*$)|(?:\s+))*[.:])`, NameClass, nil},
+			{`(?:[^\W\d]\w*)`, NameFunction, Pop(1)},
+			{`\(`, Punctuation, Pop(1)},
+		},
+		"goto": {
+			Include("ws"),
+			{`(?:[^\W\d]\w*)`, NameLabel, Pop(1)},
+		},
+		"label": {
+			Include("ws"),
+			{`::`, Punctuation, Pop(1)},
+			{`(?:[^\W\d]\w*)`, NameLabel, nil},
+		},
+		"stringescape": {
+			{`\\([abfnrtv\\"\']|[\r\n]{1,2}|z\s*|x[0-9a-fA-F]{2}|\d{1,3}|u\{[0-9a-fA-F]+\})`, LiteralStringEscape, nil},
+		},
+		"sqs": {
+			{`'`, LiteralStringSingle, Pop(1)},
+			{`[^\\']+`, LiteralStringSingle, nil},
+		},
+		"dqs": {
+			{`"`, LiteralStringDouble, Pop(1)},
+			{`[^\\"]+`, LiteralStringDouble, nil},
+		},
+	},
+))