Update WebIDL.py (#32495)

* Update WebIDL.py

* Update WebIDL.py

* Add builtin-array.patch

* Fix CodegenRust.py and Configuration.py

* Fix missing downcasts

* mach fmt

* Update check and comment to explain why we need this check

* Update Global of DissimilarOriginWindow.webidl

third_party/WebIDL/tests/test_nullable_void.py

@@ -0,0 +1,19 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface NullableVoid {
+              void? foo();
+            };
+        """
+        )
+
+        parser.finish()
+    except WebIDL.WebIDLError:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")