Move expand_acl to ACLFormatter::expand()

- including tests

src/Util/ACLFormatter.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Friendica\Util;
+
+use Friendica\Model\Group;
+
+/**
+ * Util class for ACL formatting
+ */
+final class ACLFormatter
+{
+	/**
+	 * Turn user/group ACLs stored as angle bracketed text into arrays
+	 *
+	 * @param string $ids A angle-bracketed list of IDs
+	 *
+	 * @return array The array based on the IDs
+	 */
+	public function expand(string $ids)
+	{
+		// turn string array of angle-bracketed elements into numeric array
+		// e.g. "<1><2><3>" => array(1,2,3);
+		preg_match_all('/<(' . Group::FOLLOWERS . '|'. Group::MUTUALS . '|[0-9]+)>/', $ids, $matches, PREG_PATTERN_ORDER);
+
+		return $matches[1];
+	}
+}