Add HTML Purify to BBCode::convert

- Replace previous HTML cleanup using DOMDocument
- Remove obsolete HTML::sanitizeCSS method
- Use Strings::autoLinkRegEx for PageInfo::getRelevantUrlFromBody
- Update previous tests expectations
- Add new specific XSS tests

src/Content/PageInfo.php

@@ -265,7 +265,7 @@ class PageInfo
 		}
 
 		if (!$matches && $searchNakedUrls) {
-			preg_match('~(?<=\W|^)(?<![=\]])(https?://.+)$~is', $body, $matches);
+			preg_match(Strings::autoLinkRegEx(), $body, $matches);
 			if ($matches && !Strings::endsWith($body, $matches[1])) {
 				unset($matches);
 			}