Add WC_Product::get_formatted_name()

For #2788
Add WC_Product_Variation::get_formatted_name()

For #2788
Deprecate woocommerce_get_formatted_product_name()

For #2788
Update woocommerce_get_formatted_product_name use

To use new WC_Product::get_formatted_name() function. For #2788
Update phpdoc
Merge pull request #2828 from thenbrent/formatted_product_name

Encapsulate formatted product name