refs #15271 [master] refactor multipart_set check

* add method 'isMultiPart' in SolrDefaultFincTrait to encapsulate check for top leve

module/finc/src/finc/RecordDriver/SolrDefaultFincTrait.php

@@ -460,6 +460,18 @@ trait SolrDefaultFincTrait
         return isset($this->fields['collection']) ? $this->fields['collection'] : [];
     }
 
+    /**
+     * refs #15271
+     * Check for Multipart resource record level 'set' MARC21 LEADER Pos 19
+     *
+     * @return boolean True if record has multiple parts, otherwise False
+     * @access public
+     */
+    public function isMultiPartSet()
+    {
+        return $this->getMultiPart() == 'a' ? true : false;
+    }
+
     /**
      * Get the content of field multipart_set.
      *