Non-unique names for inputs in nav-menu

[kkmuffme]

/wp-admin/nav-menus.php

e.g. in the

<form id="nav-menu-meta" class="nav-menu-meta" method="post" enctype="multipart/form-data">

If there are custom menus (e.g. WooCommerce) but possibly also only with native ones, it's possible that there are multiple different input with identical name= which will cause issues on form submit/processing.

e.g.

<input type="hidden" class="menu-item-title" name="menu-item[-1][menu-item-title]" value="Some Text"/>

I have multiple elements in the navigation that all have "menu-item[-1][menu-item-title]" as name (starting from -1 all the way up to -133 which is the number of elements in the navigation)
Also affects other elements like menu-item[-1][menu-item-url],...

This PR fixes an issue where custom menu items in the WordPress navigation menu were being generated with duplicate input names, causing potential form submission and processing issues.

Trac ticket: https://core.trac.wordpress.org/ticket/62925