Mark EntityManagerInterface::isOpen() as impure (#739)

Author: denis-korchagin95

stubs/EntityManager.stub

@@ -70,4 +70,9 @@ class EntityManager implements EntityManagerInterface
      */
     public function flush($entity = null);
 
+	/**
+	 * @return bool
+	 * @phpstan-impure
+	 */
+	public function isOpen();
 }

stubs/EntityManagerDecorator.stub

@@ -61,4 +61,9 @@ class EntityManagerDecorator implements EntityManagerInterface
 	 */
 	public function copy($entity, $deep = false);
 
+	/**
+	 * @return bool
+	 * @phpstan-impure
+	 */
+	public function isOpen();
 }

stubs/EntityManagerInterface.stub

@@ -78,4 +78,9 @@ interface EntityManagerInterface extends ObjectManager
 	 */
 	public function wrapInTransaction(callable $func);
 
+	/**
+	 * @return bool
+	 * @phpstan-impure
+	 */
+	public function isOpen();
 }