handle_add_var: Use ProductVariationResult.resolve
handle_add_var: Use ProductVariationResult.resolve

To remove import of now internal hash_combination function.

Refs SHOOP-1955

shawnadelic/shuup,akx/shoop,suutari-ai/shoop,shoopio/shoop,shawnadelic/shuup,akx/shoop,akx/shoop,shawnadelic/shuup,shoopio/shoop,shoopio/shoop,hrayr-artunyan/shuup,suutari/shoop,hrayr-artunyan/shuup,suutari/shoop,hrayr-artunyan/shuup,suutari-ai/shoop,suutari-ai/shoop,suutari/shoop