Add support for decompositions of parameterized cirq.CCZPowGate (quantumlib#5087)

* Add support for decompositions of parameterized cirq.CCZPowGate

* Add test for parameterized decomposition of CCZ

Author: tanujkhattar

cirq/ops/three_qubit_gates.py

@@ -95,9 +95,6 @@ def _decompose_(self, qubits):
 
         where p = T**self._exponent
         """
-        if protocols.is_parameterized(self):
-            return NotImplemented
-
         a, b, c = qubits
 
         # Hacky magic: avoid the non-adjacent edge.

cirq/ops/three_qubit_gates_test.py

@@ -192,6 +192,7 @@ def test_identity_multiplication():
         (cirq.CCZ(*cirq.LineQubit.range(3)), 8),
         (cirq.CCX(*cirq.LineQubit.range(3)), 8),
         (cirq.CCZ(cirq.LineQubit(0), cirq.LineQubit(2), cirq.LineQubit(1)), 8),
+        (cirq.CCZ(cirq.LineQubit(0), cirq.LineQubit(2), cirq.LineQubit(1)) ** sympy.Symbol("s"), 8),
         (cirq.CSWAP(*cirq.LineQubit.range(3)), 9),
         (cirq.CSWAP(*reversed(cirq.LineQubit.range(3))), 9),
         (cirq.CSWAP(cirq.LineQubit(1), cirq.LineQubit(0), cirq.LineQubit(2)), 12),