Decompose PhasedISwap into sycamore gates using precomputed coefficients.

This should only be called if the Gate has a phase_exponent of .25. If the gate has an exponent of 1, decompose_phased_iswap_into_syc should be used instead. Converting PhasedISwap gates to Sycamore is not supported if neither of these constraints are satisfied.

This synthesize a PhasedISwap in terms of four sycamore gates. This compilation converts the gate into a circuit involving two CZ gates, which themselves are each represented as two Sycamore gates and single-qubit rotations

theta rotation parameter
a First qubit id to operate on
b Second qubit id to operate on

a Cirq program implementing the Phased ISWAP gate