[RFC] Support for authorized payments

[Nek-]

Hello,

I figured out that authorized payments seem to be really not supported by the refund plugin.

Let me explain more precisely:

 Order checkout
┌────────────────────────┐                    ┌──────────────────────────┐
│                        │                    │                          │
│ Payment by card        │                    │     Order                │ Refund will fail
│ (stripe for me)        ├────────────────────►     (state: new)         ├─────────►
│ NOT captured           │                    │                          │
└────────────────────────┘                    └───────────┬──────────────┘
                                                          │
                                                          │ Human action:
                                                          │ stock verification etc
                                              ┌───────────▼──────────────┐
                                              │                          │
                                              │    Order                 │
                                              │    (state fulfilled)     │
                                              └───────────┬──────────────┘
                                                          │
                                                          │
                                              ┌───────────▼───────────────┐
                                              │                           │
                                              │   Payment capture         │
                                              │                           │
                                              └───────────┬───────────────┘
                                                          │
                                                          │   Any refund from here
                                                          ▼   is working

I'm not sure how critical is this issue, but when the payment is only captured, the refund page is a 500 error.

Mostly because of those 2 lines:

RefundPlugin/src/Resources/views/_paymentMethod.html.twig

Lines 2 to 3 in 09ef1e6

	{% set completed = constant('Sylius\\Component\\Core\\Model\\PaymentInterface::STATE_COMPLETED') %}
	{% set original_payment_method = order.lastPayment(completed).method %}

But it's also complicated to allow a refund on a non captured payment, because it's not really a refund: it's just a reduction of the amount to capture if not all the items are canceled (or even partially canceled).

I think there's also some issues with stock management when an item is refund but the whole order not canceled.

I'm not sure of anything here, I'm just exposing a problem that has tons of solutions...