Add method to test whether currently viewing the site home page in WP_Query

[joedolson]

Currently, WP_Query offers to methods to test the home page qualities for a site, is_front_page() and is_home(), but neither of these actually verify that this is truly the site's home page.

To test the home page, you need to check both values, compare them against the queried object ID, and verify that pagination isn't set.

While this isn't particularly complex ($is_front = ! is_paged() && ( is_front_page() || ( is_home() && ( (int) get_option( 'page_for_posts' ) !== get_queried_object_id() ) ) );), it is confusing and verbose.

Adding a method such as is_home_page() that produced this logic would make it simpler to test whether you are viewing the actual root.

See #62895 as a case where this would have been helpful for simplification.