Merge metadata & native key expressions

Do not delegates query building to Key instance anymore.

lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/KeyValue/Key.php

@@ -2,10 +2,8 @@
 
 namespace Alchemy\Phrasea\SearchEngine\Elastic\AST\KeyValue;
 
-use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryContext;
-
 interface Key
 {
-    public function buildQueryForValue($value, QueryContext $context);
+    public function getIndexField();
     public function __toString();
 }