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/a/abnf.go

@@ -0,0 +1,38 @@
+package a
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Abnf lexer.
+var Abnf = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "ABNF",
+		Aliases:   []string{"abnf"},
+		Filenames: []string{"*.abnf"},
+		MimeTypes: []string{"text/x-abnf"},
+	},
+	Rules{
+		"root": {
+			{`;.*$`, CommentSingle, nil},
+			{`(%[si])?"[^"]*"`, Literal, nil},
+			{`%b[01]+\-[01]+\b`, Literal, nil},
+			{`%b[01]+(\.[01]+)*\b`, Literal, nil},
+			{`%d[0-9]+\-[0-9]+\b`, Literal, nil},
+			{`%d[0-9]+(\.[0-9]+)*\b`, Literal, nil},
+			{`%x[0-9a-fA-F]+\-[0-9a-fA-F]+\b`, Literal, nil},
+			{`%x[0-9a-fA-F]+(\.[0-9a-fA-F]+)*\b`, Literal, nil},
+			{`\b[0-9]+\*[0-9]+`, Operator, nil},
+			{`\b[0-9]+\*`, Operator, nil},
+			{`\b[0-9]+`, Operator, nil},
+			{`\*`, Operator, nil},
+			{Words(``, `\b`, `ALPHA`, `BIT`, `CHAR`, `CR`, `CRLF`, `CTL`, `DIGIT`, `DQUOTE`, `HEXDIG`, `HTAB`, `LF`, `LWSP`, `OCTET`, `SP`, `VCHAR`, `WSP`), Keyword, nil},
+			{`[a-zA-Z][a-zA-Z0-9-]+\b`, NameClass, nil},
+			{`(=/|=|/)`, Operator, nil},
+			{`[\[\]()]`, Punctuation, nil},
+			{`\s+`, Text, nil},
+			{`.`, Text, nil},
+		},
+	},
+))