Use Stringable interface as much as possible

Author: VincentLanglet

Node/NodeInterface.php

@@ -21,11 +21,9 @@
  *
  * @internal
  */
-interface NodeInterface
+interface NodeInterface extends \Stringable
 {
     public function getNodeName(): string;
 
     public function getSpecificity(): Specificity;
-
-    public function __toString(): string;
 }