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>

templates/repo/view_file.tmpl

@@ -88,18 +88,30 @@
 					{{end}}
 				</div>
 			{{else if .FileSize}}
+				{{if .IsFileTooLarge}}
 				<table>
 					<tbody>
 						<tr>
-						{{if .IsFileTooLarge}}
 							<td><strong>{{.i18n.Tr "repo.file_too_large"}}</strong></td>
-						{{else}}
-							<td class="lines-num">{{.LineNums}}</td>
-							<td class="lines-code"><pre><code class="{{.HighlightClass}}"><ol class="linenums">{{.FileContent}}</ol></code></pre></td>
-						{{end}}
 						</tr>
 					</tbody>
 				</table>
+				{{else}}
+				<table>
+					<tbody>
+						{{range $line, $code := .FileContent}}
+						<tr>
+							<td id="L{{$line}}" class="lines-num">
+								<span id="L{{$line}}" data-line-number="{{$line}}"></span>
+							</td>
+							<td rel="L{{$line}}" class="lines-code chroma">
+								<pre><code>{{$code | Safe}}</code></pre>
+							</td>
+						</tr>
+						{{end}}
+					</tbody>
+				</table>
+				{{end}}
 			{{end}}
 		</div>
 	</div>