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/t/tablegen.go

@@ -0,0 +1,42 @@
+package t
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// TableGen lexer.
+var Tablegen = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "TableGen",
+		Aliases:   []string{"tablegen"},
+		Filenames: []string{"*.td"},
+		MimeTypes: []string{"text/x-tablegen"},
+	},
+	Rules{
+		"root": {
+			Include("macro"),
+			Include("whitespace"),
+			{`c?"[^"]*?"`, LiteralString, nil},
+			Include("keyword"),
+			{`\$[_a-zA-Z][_\w]*`, NameVariable, nil},
+			{`\d*[_a-zA-Z][_\w]*`, NameVariable, nil},
+			{`\[\{[\w\W]*?\}\]`, LiteralString, nil},
+			{`[+-]?\d+|0x[\da-fA-F]+|0b[01]+`, LiteralNumber, nil},
+			{`[=<>{}\[\]()*.,!:;]`, Punctuation, nil},
+		},
+		"macro": {
+			{`(#include\s+)("[^"]*")`, ByGroups(CommentPreproc, LiteralString), nil},
+			{`^\s*#(ifdef|ifndef)\s+[_\w][_\w\d]*`, CommentPreproc, nil},
+			{`^\s*#define\s+[_\w][_\w\d]*`, CommentPreproc, nil},
+			{`^\s*#endif`, CommentPreproc, nil},
+		},
+		"whitespace": {
+			{`(\n|\s)+`, Text, nil},
+			{`//.*?\n`, Comment, nil},
+		},
+		"keyword": {
+			{Words(``, `\b`, `bit`, `bits`, `class`, `code`, `dag`, `def`, `defm`, `field`, `foreach`, `in`, `int`, `let`, `list`, `multiclass`, `string`), Keyword, nil},
+		},
+	},
+))