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/r/rexx.go

@@ -0,0 +1,59 @@
+package r
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Rexx lexer.
+var Rexx = internal.Register(MustNewLexer(
+	&Config{
+		Name:            "Rexx",
+		Aliases:         []string{"rexx", "arexx"},
+		Filenames:       []string{"*.rexx", "*.rex", "*.rx", "*.arexx"},
+		MimeTypes:       []string{"text/x-rexx"},
+		NotMultiline:    true,
+		CaseInsensitive: true,
+	},
+	Rules{
+		"root": {
+			{`\s`, TextWhitespace, nil},
+			{`/\*`, CommentMultiline, Push("comment")},
+			{`"`, LiteralString, Push("string_double")},
+			{`'`, LiteralString, Push("string_single")},
+			{`[0-9]+(\.[0-9]+)?(e[+-]?[0-9])?`, LiteralNumber, nil},
+			{`([a-z_]\w*)(\s*)(:)(\s*)(procedure)\b`, ByGroups(NameFunction, TextWhitespace, Operator, TextWhitespace, KeywordDeclaration), nil},
+			{`([a-z_]\w*)(\s*)(:)`, ByGroups(NameLabel, TextWhitespace, Operator), nil},
+			Include("function"),
+			Include("keyword"),
+			Include("operator"),
+			{`[a-z_]\w*`, Text, nil},
+		},
+		"function": {
+			{Words(``, `(\s*)(\()`, `abbrev`, `abs`, `address`, `arg`, `b2x`, `bitand`, `bitor`, `bitxor`, `c2d`, `c2x`, `center`, `charin`, `charout`, `chars`, `compare`, `condition`, `copies`, `d2c`, `d2x`, `datatype`, `date`, `delstr`, `delword`, `digits`, `errortext`, `form`, `format`, `fuzz`, `insert`, `lastpos`, `left`, `length`, `linein`, `lineout`, `lines`, `max`, `min`, `overlay`, `pos`, `queued`, `random`, `reverse`, `right`, `sign`, `sourceline`, `space`, `stream`, `strip`, `substr`, `subword`, `symbol`, `time`, `trace`, `translate`, `trunc`, `value`, `verify`, `word`, `wordindex`, `wordlength`, `wordpos`, `words`, `x2b`, `x2c`, `x2d`, `xrange`), ByGroups(NameBuiltin, TextWhitespace, Operator), nil},
+		},
+		"keyword": {
+			{`(address|arg|by|call|do|drop|else|end|exit|for|forever|if|interpret|iterate|leave|nop|numeric|off|on|options|parse|pull|push|queue|return|say|select|signal|to|then|trace|until|while)\b`, KeywordReserved, nil},
+		},
+		"operator": {
+			{`(-|//|/|\(|\)|\*\*|\*|\\<<|\\<|\\==|\\=|\\>>|\\>|\\|\|\||\||&&|&|%|\+|<<=|<<|<=|<>|<|==|=|><|>=|>>=|>>|>|¬<<|¬<|¬==|¬=|¬>>|¬>|¬|\.|,)`, Operator, nil},
+		},
+		"string_double": {
+			{`[^"\n]+`, LiteralString, nil},
+			{`""`, LiteralString, nil},
+			{`"`, LiteralString, Pop(1)},
+			{`\n`, Text, Pop(1)},
+		},
+		"string_single": {
+			{`[^\'\n]`, LiteralString, nil},
+			{`\'\'`, LiteralString, nil},
+			{`\'`, LiteralString, Pop(1)},
+			{`\n`, Text, Pop(1)},
+		},
+		"comment": {
+			{`[^*]+`, CommentMultiline, nil},
+			{`\*/`, CommentMultiline, Pop(1)},
+			{`\*`, CommentMultiline, nil},
+		},
+	},
+))