Optimize PhaseShift, T, S gates

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Context: PauliZ has a fast implementation which relies on the sparsity of the operator in DefaultQubit. Several operations have the same non-zero matrix elements and could be similarly accelerated. One candidate is PhaseShift which is abundantly used in iterative_qpe.

Description of the Change: Port the fast-PauliZ to PhaseShift and use the implementation for PauliZ, S and T.

Benefits: Faster execution. For example the simple system

nwires = 24
dev = qml.device("default.qubit", shots=1)
@qml.qnode(dev)
def circuit(iters):
    for i in range(iters):
        qml.PhaseShift(0.1234, i % nwires)
    return qml.sample(wires=[0])
circuit(100)

takes 0m13.178s on master and 0m9.146s on optim_apply_operations. We observe the same speed-up for S and T.

Possible Drawbacks:

Related GitHub Issues:

PennyLaneAI / pennylane

Optimize PhaseShift, T, S gates #5876

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