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Add flatten option to the NLocal family (#10269)

* Add flatten option to the NLocal family

This commit adds a new flag `flatten` to the circuit library elements in
the NLocal family. This flag is used to avoid the nested wrapping of the
output that is done by default in the output of these gates. This is
done primarily in the interest of performance. The runtime
performance of bind_parameters() is vastly improved with a flattened
output compared to the nested object. For example, running:

```
qc = EfficientSU2(100, entanglement="linear", reps=100)
qc.measure_all()
qc.bind_parameters({x: math.pi / 2 for x in qc.parameters})
```

the runtime of `bind_parameters()` went from ~390 seconds with the
wrapped output to ~0.5 seconds with the flattened output. I think given
these results longer term we might want to flip the default behavior to
only wrap on user request (likely for visualization as that's the only
use case I can think of for the wrapped output). The default value
is set to `None` in this PR to facilitate this change. In 0.26/0.45 we
can emit a warning if `flatten` is `None` to warn that the default will
change in a future release.

* Add missing nlocal subclasses

* Add setter

* Fix lint

* Fix flatten for EvolvedOperatorAnsatz

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