woocommerce_variation_is_visible/is_active filter args

Amendment to #5661 

The ```woocommerce_variation_is_visible``` filter args are a bit inconsistent with the class norm and the newly introduced ```woocommerce_variation_is_active``` arguments copied that mistake.

```woocommerce_variation_is_active``` can still be fixed, since it doesn't exist in any stable release. 

It's probably too late to change ```woocommerce_variation_is_visible``` drastically, unless we deprecate the old filter and introduce a new one.