WP Simple Pay Pro (Personal) 4.5.1

* New: Add Brazil and United Arab Emirates to Stripe country list.
* Fix: Ensure step attribute is set when changing custom input type to number.
* Fix: Backport in-plugin upgrade URL fix from Lite.
* Fix: Do not output PHP warnings when visiting Payment Confirmation page directly.
* Fix: Avoid creating a duplicate Customer record when using on-site fields with Stripe Checkout.

* Fix: Do not attempt custom amount validations against legacy `plan_` objects.
* Fix: Show generic error message text when REST API response is invalid JSON.
* Fix: Restore `.toggleOverlayForm()` JavaScript API method.

* Fix: Ensure manually calculated coupon amounts return a valid integer.
* Fix: Ensure ACH Debit Subscriptions are not incorrectly redirected to Payment Failure page.