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/p/prolog.go

@@ -0,0 +1,50 @@
+package p
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Prolog lexer.
+var Prolog = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Prolog",
+		Aliases:   []string{"prolog"},
+		Filenames: []string{"*.ecl", "*.prolog", "*.pro", "*.pl"},
+		MimeTypes: []string{"text/x-prolog"},
+	},
+	Rules{
+		"root": {
+			{`/\*`, CommentMultiline, Push("nested-comment")},
+			{`%.*`, CommentSingle, nil},
+			{`0\'.`, LiteralStringChar, nil},
+			{`0b[01]+`, LiteralNumberBin, nil},
+			{`0o[0-7]+`, LiteralNumberOct, nil},
+			{`0x[0-9a-fA-F]+`, LiteralNumberHex, nil},
+			{`\d\d?\'[a-zA-Z0-9]+`, LiteralNumberInteger, nil},
+			{`(\d+\.\d*|\d*\.\d+)([eE][+-]?[0-9]+)?`, LiteralNumberFloat, nil},
+			{`\d+`, LiteralNumberInteger, nil},
+			{`[\[\](){}|.,;!]`, Punctuation, nil},
+			{`:-|-->`, Punctuation, nil},
+			{`"(?:\\x[0-9a-fA-F]+\\|\\u[0-9a-fA-F]{4}|\\U[0-9a-fA-F]{8}|\\[0-7]+\\|\\["\nabcefnrstv]|[^\\"])*"`, LiteralStringDouble, nil},
+			{`'(?:''|[^'])*'`, LiteralStringAtom, nil},
+			{`is\b`, Operator, nil},
+			{`(<|>|=<|>=|==|=:=|=|/|//|\*|\+|-)(?=\s|[a-zA-Z0-9\[])`, Operator, nil},
+			{`(mod|div|not)\b`, Operator, nil},
+			{`_`, Keyword, nil},
+			{`([a-z]+)(:)`, ByGroups(NameNamespace, Punctuation), nil},
+			{`([a-zÀ-῿぀-퟿-￯][\w$À-῿぀-퟿-￯]*)(\s*)(:-|-->)`, ByGroups(NameFunction, Text, Operator), nil},
+			{`([a-zÀ-῿぀-퟿-￯][\w$À-῿぀-퟿-￯]*)(\s*)(\()`, ByGroups(NameFunction, Text, Punctuation), nil},
+			{`[a-zÀ-῿぀-퟿-￯][\w$À-῿぀-퟿-￯]*`, LiteralStringAtom, nil},
+			{`[#&*+\-./:<=>?@\\^~¡-¿‐-〿]+`, LiteralStringAtom, nil},
+			{`[A-Z_]\w*`, NameVariable, nil},
+			{`\s+|[ -‏￰-￾￯]`, Text, nil},
+		},
+		"nested-comment": {
+			{`\*/`, CommentMultiline, Pop(1)},
+			{`/\*`, CommentMultiline, Push()},
+			{`[^*/]+`, CommentMultiline, nil},
+			{`[*/]`, CommentMultiline, nil},
+		},
+	},
+))