Confirmation of Plan Cancellation/Reactivation

[YvesCesar]

Summary

Customers could cancel or reactivate a subscription with a single click on the My Subscription page, WooCommerce Subscriptions applies the status change immediately, making accidental changes too easy.

This PR adds a server-side confirmation step before the change is applied.

How it works

• A hook on wp_loaded (priority 99) intercepts the status change request one priority before WCS_User_Change_Status_Handler (priority 100) and redirects back to the subscription page.
• A WooCommerce notice asks for confirmation ("Yes, cancel subscription" / "No, keep subscription"). Only the confirmed link passes through to the original handler, so all of its nonce and permission validation remains intact.
• Works without JavaScript.

The statuses that require confirmation are defined in a single map (libresign_get_subscription_confirmation_strings), currently cancelled and active (reactivation). New statuses can be added with one entry.