build_root_map() / post count query updated for consistency.

When wpseo_typecount_join and wpseo_typecount_where filters in build_post_type_map() function is used, the resulting root sitemap index and individual post type maps become incompatible as the number of posts included in the sitemap changes.

Changed build_root_map() function to use same query and filters used in build_post_type_map().

Note: build_post_type_map uses different join and where filters (wpseo_typecount_join and wpseo_posts_join / wpseo_typecount_where and wpseo_posts_where) for counting the number of posts and building the map. I think these filters should be same to ensure consistent results but I did not propose a change as I'm not sure if there may be other use cases utilizing different filter names.