Improve default callback for taxonomies categories/post_tag

[momo360modena]

See patch.

With the new API of taxonomies, one taxonomy can have multiples object types.

Add the param $taxonomy are now required for custom callback.

The default callback, used for category/post_tag, must be support an array of object types, because with the function register_taxonomy_for_object_type(), i can add a another custom object type to a default taxonomy.

[scribu]

Looks good.

[dd32]

(In [13625]) Add custom post_type support to _update_post_term_coun(). Props momo360modena. Fixes #12348