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/lexer.go

@@ -0,0 +1,125 @@
+package chroma
+
+import (
+	"fmt"
+)
+
+var (
+	defaultOptions = &TokeniseOptions{
+		State:    "root",
+		EnsureLF: true,
+	}
+)
+
+// Config for a lexer.
+type Config struct {
+	// Name of the lexer.
+	Name string
+
+	// Shortcuts for the lexer
+	Aliases []string
+
+	// File name globs
+	Filenames []string
+
+	// Secondary file name globs
+	AliasFilenames []string
+
+	// MIME types
+	MimeTypes []string
+
+	// Regex matching is case-insensitive.
+	CaseInsensitive bool
+
+	// Regex matches all characters.
+	DotAll bool
+
+	// Regex does not match across lines ($ matches EOL).
+	//
+	// Defaults to multiline.
+	NotMultiline bool
+
+	// Don't strip leading and trailing newlines from the input.
+	// DontStripNL bool
+
+	// Strip all leading and trailing whitespace from the input
+	// StripAll bool
+
+	// Make sure that the input ends with a newline. This
+	// is required for some lexers that consume input linewise.
+	EnsureNL bool
+
+	// If given and greater than 0, expand tabs in the input.
+	// TabSize int
+
+	// Priority of lexer.
+	//
+	// If this is 0 it will be treated as a default of 1.
+	Priority float32
+}
+
+// Token output to formatter.
+type Token struct {
+	Type  TokenType `json:"type"`
+	Value string    `json:"value"`
+}
+
+func (t *Token) String() string   { return t.Value }
+func (t *Token) GoString() string { return fmt.Sprintf("&Token{%s, %q}", t.Type, t.Value) }
+
+// Clone returns a clone of the Token.
+func (t *Token) Clone() Token {
+	return *t
+}
+
+// EOF is returned by lexers at the end of input.
+var EOF Token
+
+// TokeniseOptions contains options for tokenisers.
+type TokeniseOptions struct {
+	// State to start tokenisation in. Defaults to "root".
+	State string
+	// Nested tokenisation.
+	Nested bool
+
+	// If true, all EOLs are converted into LF
+	// by replacing CRLF and CR
+	EnsureLF bool
+}
+
+// A Lexer for tokenising source code.
+type Lexer interface {
+	// Config describing the features of the Lexer.
+	Config() *Config
+	// Tokenise returns an Iterator over tokens in text.
+	Tokenise(options *TokeniseOptions, text string) (Iterator, error)
+}
+
+// Lexers is a slice of lexers sortable by name.
+type Lexers []Lexer
+
+func (l Lexers) Len() int           { return len(l) }
+func (l Lexers) Swap(i, j int)      { l[i], l[j] = l[j], l[i] }
+func (l Lexers) Less(i, j int) bool { return l[i].Config().Name < l[j].Config().Name }
+
+// PrioritisedLexers is a slice of lexers sortable by priority.
+type PrioritisedLexers []Lexer
+
+func (l PrioritisedLexers) Len() int      { return len(l) }
+func (l PrioritisedLexers) Swap(i, j int) { l[i], l[j] = l[j], l[i] }
+func (l PrioritisedLexers) Less(i, j int) bool {
+	ip := l[i].Config().Priority
+	if ip == 0 {
+		ip = 1
+	}
+	jp := l[j].Config().Priority
+	if jp == 0 {
+		jp = 1
+	}
+	return ip > jp
+}
+
+// Analyser determines how appropriate this lexer is for the given text.
+type Analyser interface {
+	AnalyseText(text string) float32
+}