Networks and Sites: Introduce `populate_site_meta` filter.

The `populate_site_meta` filter can be used to modify the site meta added during the creation of a new site. This filter mirrors the approach used for networks in `populate_network_meta`.

Props spacedmonkey, davidbaumwald.
Fixes #46437.
Built from https://develop.svn.wordpress.org/trunk@44912


git-svn-id: http://core.svn.wordpress.org/trunk@44743 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/schema.php

@@ -1316,8 +1316,18 @@ function populate_site_meta( $site_id, array $meta = array() ) {
 		return;
 	}
 
+	/**
+	 * Filters meta for a site on creation.
+	 *
+	 * @since 5.2.0
+	 *
+	 * @param array $meta    Associative array of site meta keys and values to be inserted.
+	 * @param int   $site_id ID of site to populate.
+	 */
+	$site_meta = apply_filters( 'populate_site_meta', $meta, $site_id );
+
 	$insert = '';
-	foreach ( $meta as $meta_key => $meta_value ) {
+	foreach ( $site_meta as $meta_key => $meta_value ) {
 		if ( is_array( $meta_value ) ) {
 			$meta_value = serialize( $meta_value );
 		}

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.2-alpha-44911';
+$wp_version = '5.2-alpha-44912';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.