WooCommerce Order Status Manager 1.15.6

* Fix - "Translation triggered too early" errors
* Dev - Update the SkyVerge framework to v5.15.9
* Misc - Removed deprecated usage of WC_Email `$find` and `$replace` properties in favor of `$placeholder`. The associated filters `wc_order_status_manager_order_status_email_find_variables` and `wc_order_status_manager_order_status_email_replace_variables` have also been deprecated, with a new replacement: `wc_order_status_manager_order_status_email_placeholders`
* Tweak - When an order moves to a custom paid status, we no longer delete the existing `woocommerce_downloadable_product_permissions` record for that order. Our new behavior better aligns with WooCommerce core paid statuses.

* Fix - The `wc-checkout-draft` status has been automatically updated to change its "Paid" setting to "Orders with this status require payment". This fixes issues with block checkout for some gateways.

* Fix - Ensure Font Awesome icons are loaded on orders list page when HPOS is enabled
* Fix - Ensure order line items appear in custom emails that are dispatched when a new order is created
* Fix - Address PHP warnings when emails are sent
* Fix - Ensures custom image icons are kept in place when status changes are made

Misc - Add compatibility for WooCommerce High Performance Order Storage (HPOS)

* Misc - Require PHP 7.4 and WordPress 5.6