Payment operations

We should leverage #1839516: Introduce entity operation providers.

As we have a number of different operations, and more may be added by payment method plugins, these should be dynamic. In order to let plugins provide them, add the following three methods:

\Drupal\payment\PaymentProcessingInterface::paymentOperations()

Returns operations names and labels.

\Drupal\payment\PaymentProcessingInterface::paymentOperationAccess(PaymentInterface $payment, $operation)

Checks if an operation can be performed on a payment.

\Drupal\payment\PaymentProcessingInterface::executePaymentOperation(PaymentInterface $payment, $operation)

Performs the operation after calling paymentOperationAccess() first.

This will replace PaymentProcessingInterface::validatePayment(), PaymentProcessingInterface::executePayment(), Payment::execute(), and part of Payment::validate().

The future PaymentListController::getOperations() can then call Payment::getPaymentMethod()->getPlugin()->paymentOperations() and merge those with the default entity operations for use in the UI later on.

Note that this also replaces hook_payment_validate() and the corresponding Rules event. Next to that, operations should have a flag to indicate whether or not they need a permission to be generated for them.

Follow-up: #2037071: Make "execute" operation part of PaymentProcessingInterface.