Expose reformatted parameters

[arcondello]

The StructuredSolver._format_params method currently transforms the initial_state parameter from a dict to the format expected by the endpoint.

This translation, while useful for the user, makes it hard for other libraries (e.g. aws-braket-ocean-plugin) that are trying to mock the behavior of the DWaveSampler from dwave-system to do so.

It would be helpful to expose this logic in a way that can be used by other libraries. Some possible approaches:

1. Change the _format_params method to a public class method, or even a static method. This would allow users/libaries to use the method without needing to authenticate with D-Wave.
2. Move _format_parmas to the DWaveSampler level, and expose it as a public method. We would likely want to deprecate the method in the cloud-client.

I am inclined towards (2).

[JoelPasvolsky]

2 makes sense to me given that the transformation is specific to QPU. Where would it live in 1? Also I think with 1 it would need renaming, but that may be true for 2 also

[randomir]

Keeping this particular function in the cloud client makes sense to me. Why? Because it translates a nice state map into a list with 3's - very SAPI-specific, low-level and ugly.

This is related to #166 and #199.

I'd say, ideally, we don't use SAPI-specific data encoding anywhere on the client's API surface, and the translation happens internally.