Polarized SANS metadata: add SavePolarizedNXcanSAS to SANSSave

[rbauststfc]

Part of #36147. See the design and requirements documents, and the NXcanSAS specification proposal, that are linked on that issue for more context and details of what needs to be implemented.

After adding a new SavePolarizedNXcanSAS algorithm we need to add it to the SANSSave algorithm. This will be the first step towards integrating this new save option into the SANS reduction.

The SavePolarizedNXcanSAS algorithm will have quite a lot of new input properties. To avoid adding this long list to SANSSave, we should investigate adding just a single additional property that will take a dictionary of the polarized metadata property values to be passed to SavePolarizedNXcanSAS. This would be something like the MergeRunsOptions property on the LoadAndMerge algorithm. We would need to pass a nested dictionary to SANSSave, which I think should be fine from a technical perspective, but we’ll need to double check.

From a usability perspective this approach is still not ideal, but I think we will expect people to use SavePolarizedNXcanSAS if they are using a save algorithm directly in their own scripts. From a maintainability perspective, this approach will hopefully make it easier to maintain and support developments to the SANS save algorithms in the future.

This issue should not be worked on until #38505 has been completed.