Support inverse gate JSON seralization (#6912)

Implement serialization of `_InverseCompositeGate`.

Fixes #6769

Author: justinpan0

cirq-core/cirq/json_resolver_cache.py

@@ -150,6 +150,7 @@ def _symmetricalqidpair(qids):
         'IdentityGate': cirq.IdentityGate,
         'InitObsSetting': cirq.work.InitObsSetting,
         'InsertionNoiseModel': InsertionNoiseModel,
+        '_InverseCompositeGate': raw_types._InverseCompositeGate,
         'KeyCondition': cirq.KeyCondition,
         'KrausChannel': cirq.KrausChannel,
         'LinearDict': cirq.LinearDict,

cirq-core/cirq/ops/gate_operation_test.py

@@ -506,7 +506,6 @@ def all_subclasses(cls):
         cirq.transformers.measurement_transformers._ConfusionChannel,
         cirq.transformers.measurement_transformers._ModAdd,
         cirq.transformers.routing.visualize_routed_circuit._SwapPrintGate,
-        cirq.ops.raw_types._InverseCompositeGate,
         cirq.circuits.qasm_output.QasmTwoQubitGate,
         cirq.ops.MSGate,
         # Interop gates

cirq-core/cirq/ops/raw_types.py

@@ -1066,6 +1066,9 @@ def __repr__(self) -> str:
     def __str__(self) -> str:
         return f'{self._original!s}†'
 
+    def _json_dict_(self) -> Dict[str, Any]:
+        return {'original': self._original}
+
 
 def _validate_qid_shape(val: Any, qubits: Sequence['cirq.Qid']) -> None:
     """Helper function to validate qubits for gates and operations.

cirq-core/cirq/protocols/json_test_data/_InverseCompositeGate.json

@@ -0,0 +1,10 @@
+{
+    "cirq_type": "_InverseCompositeGate",
+    "original": {
+        "cirq_type": "QubitPermutationGate",
+        "permutation": [
+        0,
+        1,
+        2
+    ]}
+}

cirq-core/cirq/protocols/json_test_data/_InverseCompositeGate.repr

@@ -0,0 +1 @@
+(cirq.QubitPermutationGate(permutation=(0, 1, 2))**-1)