Restore the "Product using variations" views relationship so variations can be sorted by their order on the product

Describe your bug or feature request.

Views of product variations can't be ordered the way the variations are ordered on their product.

If a bug, provide steps to reproduce it from a clean install.

• Create a view of product variations with the "Product" relationship and add the "Order by delta (using variations)" sort.
• Reorder the product's variations. The view still lists them in variation ID order.