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/i/io.go

@@ -0,0 +1,40 @@
+package i
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Io lexer.
+var Io = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Io",
+		Aliases:   []string{"io"},
+		Filenames: []string{"*.io"},
+		MimeTypes: []string{"text/x-iosrc"},
+	},
+	Rules{
+		"root": {
+			{`\n`, Text, nil},
+			{`\s+`, Text, nil},
+			{`//(.*?)\n`, CommentSingle, nil},
+			{`#(.*?)\n`, CommentSingle, nil},
+			{`/(\\\n)?[*](.|\n)*?[*](\\\n)?/`, CommentMultiline, nil},
+			{`/\+`, CommentMultiline, Push("nestedcomment")},
+			{`"(\\\\|\\"|[^"])*"`, LiteralString, nil},
+			{`::=|:=|=|\(|\)|;|,|\*|-|\+|>|<|@|!|/|\||\^|\.|%|&|\[|\]|\{|\}`, Operator, nil},
+			{`(clone|do|doFile|doString|method|for|if|else|elseif|then)\b`, Keyword, nil},
+			{`(nil|false|true)\b`, NameConstant, nil},
+			{`(Object|list|List|Map|args|Sequence|Coroutine|File)\b`, NameBuiltin, nil},
+			{`[a-zA-Z_]\w*`, Name, nil},
+			{`(\d+\.?\d*|\d*\.\d+)([eE][+-]?[0-9]+)?`, LiteralNumberFloat, nil},
+			{`\d+`, LiteralNumberInteger, nil},
+		},
+		"nestedcomment": {
+			{`[^+/]+`, CommentMultiline, nil},
+			{`/\+`, CommentMultiline, Push()},
+			{`\+/`, CommentMultiline, Pop(1)},
+			{`[+/]`, CommentMultiline, nil},
+		},
+	},
+))