Show the order summary on the booking payment landing page

Frank Mablyrequested to merge
issue/yoyaku-3612895:3612895-show-the-order into 1.x

Fills the orchestra payment summary seam (issue 3612890) in BookingPayableResolver from the order, reusing OrderSummaryBuilder (the same breakdown the confirmation email uses: grouped by event, each ticket and price). The payment landing page then shows the order above the amount due. Kernel test PaymentSummaryResolverTest asserts the resolved Payable carries the summary (fails without the change).

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