Consider all-false invert_mask equal to no invert_mask (#6952)

Author: daxfohl

cirq-core/cirq/ops/measurement_gate.py

@@ -273,7 +273,7 @@ def _value_equality_values_(self) -> Any:
             (idxs, tuple(v for _, v in np.ndenumerate(cmap)))
             for idxs, cmap in self._confusion_map.items()
         )
-        return self.key, self.invert_mask, self._qid_shape, hashable_cmap
+        return self.key, self.full_invert_mask(), self._qid_shape, hashable_cmap
 
     def _json_dict_(self) -> Dict[str, Any]:
         other: Dict[str, Any] = {}

cirq-core/cirq/ops/measurement_gate_test.py

@@ -74,11 +74,11 @@ def test_measurement_eq():
     eq.make_equality_group(
         lambda: cirq.MeasurementGate(1, 'a'),
         lambda: cirq.MeasurementGate(1, 'a', invert_mask=()),
+        lambda: cirq.MeasurementGate(1, 'a', invert_mask=(False,)),
         lambda: cirq.MeasurementGate(1, 'a', qid_shape=(2,)),
         lambda: cirq.MeasurementGate(1, 'a', confusion_map={}),
     )
     eq.add_equality_group(cirq.MeasurementGate(1, 'a', invert_mask=(True,)))
-    eq.add_equality_group(cirq.MeasurementGate(1, 'a', invert_mask=(False,)))
     eq.add_equality_group(
         cirq.MeasurementGate(1, 'a', confusion_map={(0,): np.array([[0, 1], [1, 0]])})
     )