refs #21122 [finc] get all institution isils

* introduced function to read solr institution field

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

@@ -1077,6 +1077,16 @@ trait SolrDefaultFincTrait
             $this->fields['imprint'] : '';
     }
 
+    /**
+     * Get the item's institutions isils.
+     *
+     * @return array
+     */
+    public function getInstitutionIsils()
+    {
+        return $this->fields['institution'] ?? [];
+    }
+
     /**
      * Get the item's place of publication.
      *