Temp facet tree

[tharropoulos]

Change Summary

• fix nested reference facet_by parsing so nested facets are preserved recursively instead of being flattened to the terminal collection
  • store nested facet wrapper metadata in facet, closer to nested include_fields / ref_include_exclude_fields
• add regression tests for products -> variants -> stock nested faceting like in Facet by a nested join field leads to issues #2863

PR Checklist

• I have read and signed the Contributor License Agreement.