Multisite: move get_current_site() to load.php so that it can be used in more places, instead of importing global $current_site.

See #37699.

Built from https://develop.svn.wordpress.org/trunk@38388


git-svn-id: http://core.svn.wordpress.org/trunk@38329 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/load.php

@@ -1059,3 +1059,22 @@ function wp_doing_ajax() {
 function is_wp_error( $thing ) {
 	return ( $thing instanceof WP_Error );
 }
+
+/**
+ * Get the current network.
+ *
+ * Returns an object containing the 'id', 'domain', 'path', and 'site_name'
+ * properties of the network being viewed.
+ *
+ * @see wpmu_current_site()
+ *
+ * @since MU
+ *
+ * @global WP_Network $current_site
+ *
+ * @return WP_Network
+ */
+function get_current_site() {
+	global $current_site;
+	return $current_site;
+}