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/x/xml.go

@@ -0,0 +1,45 @@
+package x
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// XML lexer.
+var XML = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "XML",
+		Aliases:   []string{"xml"},
+		Filenames: []string{"*.xml", "*.xsl", "*.rss", "*.xslt", "*.xsd", "*.wsdl", "*.wsf", "*.svg"},
+		MimeTypes: []string{"text/xml", "application/xml", "image/svg+xml", "application/rss+xml", "application/atom+xml"},
+		DotAll:    true,
+	},
+	Rules{
+		"root": {
+			{`[^<&]+`, Text, nil},
+			{`&\S*?;`, NameEntity, nil},
+			{`\<\!\[CDATA\[.*?\]\]\>`, CommentPreproc, nil},
+			{`<!--`, Comment, Push("comment")},
+			{`<\?.*?\?>`, CommentPreproc, nil},
+			{`<![^>]*>`, CommentPreproc, nil},
+			{`<\s*[\w:.-]+`, NameTag, Push("tag")},
+			{`<\s*/\s*[\w:.-]+\s*>`, NameTag, nil},
+		},
+		"comment": {
+			{`[^-]+`, Comment, nil},
+			{`-->`, Comment, Pop(1)},
+			{`-`, Comment, nil},
+		},
+		"tag": {
+			{`\s+`, Text, nil},
+			{`[\w.:-]+\s*=`, NameAttribute, Push("attr")},
+			{`/?\s*>`, NameTag, Pop(1)},
+		},
+		"attr": {
+			{`\s+`, Text, nil},
+			{`".*?"`, LiteralString, Pop(1)},
+			{`'.*?'`, LiteralString, Pop(1)},
+			{`[^\s>]+`, LiteralString, Pop(1)},
+		},
+	},
+))

vendor/github.com/alecthomas/chroma/lexers/x/xorg.go

@@ -0,0 +1,25 @@
+package x
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Xorg lexer.
+var Xorg = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Xorg",
+		Aliases:   []string{"xorg.conf"},
+		Filenames: []string{"xorg.conf"},
+		MimeTypes: []string{},
+	},
+	Rules{
+		"root": {
+			{`\s+`, TextWhitespace, nil},
+			{`#.*$`, Comment, nil},
+			{`((|Sub)Section)(\s+)("\w+")`, ByGroups(KeywordNamespace, LiteralStringEscape, TextWhitespace, LiteralStringEscape), nil},
+			{`(End(|Sub)Section)`, KeywordNamespace, nil},
+			{`(\w+)(\s+)([^\n#]+)`, ByGroups(NameKeyword, TextWhitespace, LiteralString), nil},
+		},
+	},
+))