Add a return type extension for `WP_Query->query()` and `WP_Query->get_posts()`

[johnbillion]

Return type extension for WP_Query->query() and WP_Query->get_posts().

As get_posts() ultimately calls WP_Query->query() and WP_Query->get_posts(), they all share the same return type pattern. Not sure if you want to combine them somehow.