Networks and Sites: Introduce `network_site_info_form` action.

The action fires at the end of the site info form in network admin, and complements the existing `network_site_new_form` action.

Props virgodesign.
Fixes #50704.
Built from https://develop.svn.wordpress.org/trunk@49199


git-svn-id: http://core.svn.wordpress.org/trunk@48961 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/network/site-info.php

@@ -202,7 +202,19 @@ if ( ! empty( $messages ) ) {
 			</td>
 		</tr>
 	</table>
-	<?php submit_button(); ?>
+
+	<?php
+	/**
+	 * Fires at the end of the site info form in network admin.
+	 *
+	 * @since 5.6.0
+	 *
+	 * @param int $id The site ID.
+	 */
+	do_action( 'network_site_info_form', $id );
+
+	submit_button();
+	?>
 </form>
 
 </div>

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-alpha-49198';
+$wp_version = '5.6-alpha-49199';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.