Blockified Single Product Template: inject the product-specific classes like WooCommerce Core

[gigitux]

WooCommerce Core adds product-specific classes on the div wrapper with the function wc_product_post_class (source code).

Currently, the Blockified Single Product Template doesn't add them, and for this reason, it is necessary to do weird workarounds for adding custom styles on specific products woocommerce/woocommerce#42356.

For this reason, we want to append those classes on the body via this filter.