Set default payment processor at paymentform level
Created by: mattwire
This is currently set at a lower level on the registration/contribution forms. But it makes more sense to do it here and will mean that code can be removed at a lower level. This is required for #17508 and means we don't need to implement default handling there.
Payment processor default defined at lower form level.
Payment processor default defined at core_form level so all forms implementing payment processor selectors benefit.