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/c/ceylon.go

@@ -0,0 +1,63 @@
+package c
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Ceylon lexer.
+var Ceylon = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Ceylon",
+		Aliases:   []string{"ceylon"},
+		Filenames: []string{"*.ceylon"},
+		MimeTypes: []string{"text/x-ceylon"},
+		DotAll:    true,
+	},
+	Rules{
+		"root": {
+			{`^(\s*(?:[a-zA-Z_][\w.\[\]]*\s+)+?)([a-zA-Z_]\w*)(\s*)(\()`, ByGroups(UsingSelf("root"), NameFunction, Text, Operator), nil},
+			{`[^\S\n]+`, Text, nil},
+			{`//.*?\n`, CommentSingle, nil},
+			{`/\*`, CommentMultiline, Push("comment")},
+			{`(shared|abstract|formal|default|actual|variable|deprecated|small|late|literal|doc|by|see|throws|optional|license|tagged|final|native|annotation|sealed)\b`, NameDecorator, nil},
+			{`(break|case|catch|continue|else|finally|for|in|if|return|switch|this|throw|try|while|is|exists|dynamic|nonempty|then|outer|assert|let)\b`, Keyword, nil},
+			{`(abstracts|extends|satisfies|super|given|of|out|assign)\b`, KeywordDeclaration, nil},
+			{`(function|value|void|new)\b`, KeywordType, nil},
+			{`(assembly|module|package)(\s+)`, ByGroups(KeywordNamespace, Text), nil},
+			{`(true|false|null)\b`, KeywordConstant, nil},
+			{`(class|interface|object|alias)(\s+)`, ByGroups(KeywordDeclaration, Text), Push("class")},
+			{`(import)(\s+)`, ByGroups(KeywordNamespace, Text), Push("import")},
+			{`"(\\\\|\\"|[^"])*"`, LiteralString, nil},
+			{`'\\.'|'[^\\]'|'\\\{#[0-9a-fA-F]{4}\}'`, LiteralStringChar, nil},
+			{"\".*``.*``.*\"", LiteralStringInterpol, nil},
+			{`(\.)([a-z_]\w*)`, ByGroups(Operator, NameAttribute), nil},
+			{`[a-zA-Z_]\w*:`, NameLabel, nil},
+			{`[a-zA-Z_]\w*`, Name, nil},
+			{`[~^*!%&\[\](){}<>|+=:;,./?-]`, Operator, nil},
+			{`\d{1,3}(_\d{3})+\.\d{1,3}(_\d{3})+[kMGTPmunpf]?`, LiteralNumberFloat, nil},
+			{`\d{1,3}(_\d{3})+\.[0-9]+([eE][+-]?[0-9]+)?[kMGTPmunpf]?`, LiteralNumberFloat, nil},
+			{`[0-9][0-9]*\.\d{1,3}(_\d{3})+[kMGTPmunpf]?`, LiteralNumberFloat, nil},
+			{`[0-9][0-9]*\.[0-9]+([eE][+-]?[0-9]+)?[kMGTPmunpf]?`, LiteralNumberFloat, nil},
+			{`#([0-9a-fA-F]{4})(_[0-9a-fA-F]{4})+`, LiteralNumberHex, nil},
+			{`#[0-9a-fA-F]+`, LiteralNumberHex, nil},
+			{`\$([01]{4})(_[01]{4})+`, LiteralNumberBin, nil},
+			{`\$[01]+`, LiteralNumberBin, nil},
+			{`\d{1,3}(_\d{3})+[kMGTP]?`, LiteralNumberInteger, nil},
+			{`[0-9]+[kMGTP]?`, LiteralNumberInteger, nil},
+			{`\n`, Text, nil},
+		},
+		"class": {
+			{`[A-Za-z_]\w*`, NameClass, Pop(1)},
+		},
+		"import": {
+			{`[a-z][\w.]*`, NameNamespace, Pop(1)},
+		},
+		"comment": {
+			{`[^*/]`, CommentMultiline, nil},
+			{`/\*`, CommentMultiline, Push()},
+			{`\*/`, CommentMultiline, Pop(1)},
+			{`[*/]`, CommentMultiline, nil},
+		},
+	},
+))