Add support to group multiple gates together as one step in animated Wigner function

[tjstavenger-pnnl]

From Kevin:

I am trying to animate the Wigner function as it evolves under the Jaynes-Cummings Hamiltonian. This evolution is not a native gate, though, and has to be realized with the composite sequence:

circuit.cv_r(...)
circuit.rz(...)
circuit.cv_c_r(...)

If I understand the animate_wigner function correctly, it will break each gate into individual segments, take snapshots, and stitch them together. But these gates all commute and what I am really doing is synthesizing a composite gate, and it is that composite gate that I want to animate. The animation won’t treat it like that, and instead will animate each sequentially. Any ideas about how to get around this? It’s not a big deal if not, I can just remove this part from the tutorial.

[tjstavenger-pnnl]

closed by PR #63