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/h/hcl.go

@@ -0,0 +1,69 @@
+package h
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// HCL lexer.
+var HCL = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "HCL",
+		Aliases:   []string{"hcl"},
+		Filenames: []string{"*.hcl"},
+		MimeTypes: []string{"application/x-hcl"},
+	},
+	Rules{
+		"root": {
+			Include("string"),
+			Include("punctuation"),
+			Include("curly"),
+			Include("basic"),
+			Include("whitespace"),
+			{`[0-9]+`, LiteralNumber, nil},
+		},
+		"basic": {
+			{Words(`\b`, `\b`, `true`, `false`), KeywordType, nil},
+			{`\s*/\*`, CommentMultiline, Push("comment")},
+			{`\s*#.*\n`, CommentSingle, nil},
+			{`(.*?)(\s*)(=)`, ByGroups(Name, Text, Operator), nil},
+			{`\d+`, Number, nil},
+			{`\b\w+\b`, Keyword, nil},
+			{`\$\{`, LiteralStringInterpol, Push("var_builtin")},
+		},
+		"function": {
+			{`(\s+)(".*")(\s+)`, ByGroups(Text, LiteralString, Text), nil},
+			Include("punctuation"),
+			Include("curly"),
+		},
+		"var_builtin": {
+			{`\$\{`, LiteralStringInterpol, Push()},
+			{Words(`\b`, `\b`, `concat`, `file`, `join`, `lookup`, `element`), NameBuiltin, nil},
+			Include("string"),
+			Include("punctuation"),
+			{`\s+`, Text, nil},
+			{`\}`, LiteralStringInterpol, Pop(1)},
+		},
+		"string": {
+			{`(".*")`, ByGroups(LiteralStringDouble), nil},
+		},
+		"punctuation": {
+			{`[\[\](),.]`, Punctuation, nil},
+		},
+		"curly": {
+			{`\{`, TextPunctuation, nil},
+			{`\}`, TextPunctuation, nil},
+		},
+		"comment": {
+			{`[^*/]`, CommentMultiline, nil},
+			{`/\*`, CommentMultiline, Push()},
+			{`\*/`, CommentMultiline, Pop(1)},
+			{`[*/]`, CommentMultiline, nil},
+		},
+		"whitespace": {
+			{`\n`, Text, nil},
+			{`\s+`, Text, nil},
+			{`\\\n`, Text, nil},
+		},
+	},
+))