I18N: Adjust translator comments in nav-menu.js.

Includes:
* Moving the comments directly above `wp.i18n._x()` so that they can be picked up properly.
* Simplifying the context to avoid unnecessarily translating the string twice for the same use case.
* Using the established translator comments format for consistency.

Follow-up to [59428].

See #62402.
Built from https://develop.svn.wordpress.org/trunk@59431


git-svn-id: http://core.svn.wordpress.org/trunk@58817 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/nav-menu.js

@@ -364,9 +364,9 @@
 									if ( i == itemPosition ) { 
 										$selected = 'selected';
 									}
-									// Translators: %1$s is the current menu item number, %2$s is the total number of menu items.
 									var itemString = wp.i18n.sprintf( 
-										wp.i18n._x( '%1$s of %2$s', 'indicating a part of a total number of items in a navigation menu' ),
+										/* translators: 1: The current menu item number, 2: The total number of menu items. */
+										wp.i18n._x( '%1$s of %2$s', 'part of a total number of menu items' ),
 										i,
 										totalMenuItems
 									);
@@ -386,9 +386,9 @@
 									if ( i == itemPosition ) {
 										$selected = 'selected';
 									}
-									// Translators: %1$s is the current submenu item number, %2$s is the total number of submenu items.
 									var submenuString = wp.i18n.sprintf( 
-										wp.i18n._x( '%1$s of %2$s', 'indicating a part of a total number of items in a submenu' ),
+										/* translators: 1: The current submenu item number, 2: The total number of submenu items. */
+										wp.i18n._x( '%1$s of %2$s', 'part of a total number of menu items' ),
 										i,
 										totalSubMenuItems
 									);