Wishlist hidden product cache not cleared on visibility change

[erik-perri]

Can the hidden product cache be cleared when product visibility changes (yith_wcwl_hidden_products)? It is currently fixed to 30 days which caused an issue on a store that is only enabled once a year and hides their products in between the enabled periods.

I wasn't sure where you might want the hook to live, or if there was a reason you might not want the hook in general, so I held off on creating a PR for the change. I think the woocommerce_product_set_visibility hook can be used to know when to clear the cache.