Changes proposed in this Pull Request:

1. Populates the post_type property of WP_Screen when on an order-related admin screen with custom order tables set to authoritative, for better consistency between the posts UI and the COT UI.
2. Adds the public is_order_screen method to the Orders PageController class, which can be used to check if the current admin screen is an order-related screen, regardless of which tables are authoritative.
3. Adds helper methods to OrderUtil to check for specific order-related admin screens.

Fixes #37484

How to test the changes in this Pull Request:

This PR introduces new utility functions, but doesn't use them anywhere in the existing codebase. So one good way to test the new functions is with a simple mu-plugin. Add the following snippet to a new file in the wp-content/mu-plugins directory:

<?php

use Automattic\WooCommerce\Internal\Admin\Orders\PageController;
use Automattic\WooCommerce\Utilities\OrderUtil;

add_action(
	'admin_notices',
	function() {
		$page_controller = wc_get_container()->get( PageController::class );
		echo '<div class="notice"><pre>';
		printf( "Any order screen: %s\n", $page_controller->is_order_screen() ? 'true' : 'false' );
		printf( "Order list table: %s\n", OrderUtil::is_order_list_table_screen() ? 'true' : 'false' );
		printf( "Edit order: %s\n", OrderUtil::is_order_edit_screen() ? 'true' : 'false' );
		printf( "New order: %s\n", OrderUtil::is_new_order_screen() ? 'true' : 'false' );
		echo '</pre></div>';
	}
);

This will add a notice to the top of many pages in WP Admin that shows the results of running each of the new utility functions (notably, block editor screens will not show this notice).

1. Turn on custom order tables. In WP Admin navigate to WooCommerce > Settings > Advanced > Features. Check the box for "Enable the high performance order storage feature" and save changes. Then click the link for Custom data stores. Check the box for "Keep the posts table and the orders tables synchronized" and choose "Use the WooCommerce orders tables". Save changes.
2. Now navigate to WooCommerce > Orders and check that the results in the admin notice are accurate. Try editing an existing order and creating a new order and check the results there as well.
3. Navigate to some other areas of WP Admin that are unrelated to orders. All of the results in the admin notice should be false.
4. Now switch the custom order tables to that the Posts table is authoritative. Navigate to WooCommerce > Settings > Advanced > Custom data stores. Choose "Use the WordPress posts table" and save changes.
5. Now try going back to all the same screens as the first time around, and make sure the results in the admin notice are still accurate.