Prime users cache in WP_Query and post REST API controller.

For a call to `WP_Query` or a post REST API request that contains posts from multiple authors, call the `cache_users` function, to ensure that all user data for post authors is primed in 
a single database query. This results in far fewer database queries on multiple author sites. 

Props spacedmonkey, timothyblynjacobs, peterwilsoncc.
Fixes #55716.


git-svn-id: https://develop.svn.wordpress.org/trunk@53482 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php

@@ -369,6 +369,8 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 
 		$posts = array();
 
+		update_post_author_caches( $query_result );
+
 		foreach ( $query_result as $post ) {
 			if ( ! $this->check_read_permission( $post ) ) {
 				continue;