FSim and PhasedFSim angles should be canonicalized between (-pi, pi] / [-pi, pi) instead of [-pi, pi]

[tanujkhattar]

Description of the issue
Right now, cirq.FSimGate and cirq.PhasedFSimGate canonicalize their angles between [-pi, pi], which was done as part of #3542.

The problem with this approach is that we need to implement additional logic at the call site to check whether two instances of FSimGate are equal, instead of simply using the equality operator.

We should modify the canonicalization to be open on one of the boundaries so that the comparison at call sites can simply rely on the default value equality.

How to reproduce the issue

>>> op1, op2 = cirq.FSimGate(0, np.pi), cirq.FSimGate(0, -np.pi)
>>> op1 == op2, np.allclose(cirq.unitary(op1), cirq.unitary(op2))
(False, True)

Cirq version
0.13.0dev