[py] Add missing 'id' property to ShadowRoot class (#15739)

Author: cgoldberg

py/selenium/webdriver/remote/shadowroot.py

@@ -39,6 +39,10 @@ def __repr__(self) -> str:
             type(self), self.session.session_id, self._id
         )
 
+    @property
+    def id(self) -> str:
+        return self._id
+
     def find_element(self, by: str = By.ID, value: str = None):
         """Find an element inside a shadow root given a By strategy and
         locator.