[4.x] Add helper arg for addons to easily remove child item in core nav

[jesseleite]

This PR adds ability for an addon to remove specific core nav item children more easily. For example, in our Shopify rad pack addon, @ryanmitchell is wanting to remove the Products collection item from Collections, because that item is being listed as a child of the Shopify nav item instead.

Before

Nav::extend(function ($nav) {
    $collectionsNav = $nav->content('Collections');

    $children = $collectionsNav
        ->resolveChildren()
        ->children()
        ->reject(function ($item) {
            if (in_array($item->display(), ['Products', 'Variants'])) {
                return true;
            }
        });

    $collectionsNav->children($children);
});

After

Nav::extend(function ($nav) {
    $nav->remove('Content', 'Collections', 'Products');
    $nav->remove('Content', 'Collections', 'Variants');
});

Todo

• Add new helper arg to remove()
• Update docs
  • Document new third remove() param for removing child nav items docs#1126
  • Of course, any addon using this new 3rd remove() param, would need to explicitly require whatever version of Statamic this is tagged in, since this is a new feature 👍
    • Should min version requirement be mentioned in docs, @jasonvarga?

[jasonvarga]

Should min version requirement be mentioned in docs

Nope