Is there documentation for objects returned by WP_Query?

The tag objects returned by get_the_tags() use WP_term class. You can see this by inspecting the function’s source. The class is mentioned on the last line of the comment.

function get_the_tags( $id = 0 ) {

    /**
     * Filters the array of tags for the given post.
     *
     * @since 2.3.0
     *
     * @see get_the_terms()
     *
     * @param WP_Term[] $terms An array of tags for the given post.
     */
    return apply_filters( 'get_the_tags', get_the_terms( $id, 'post_tag' ) );
}