Calculating a cart line sell price

The cart line sell price is calculated in the IPopulateValidateCartPipeline plugin.

The following messages are generated when calculating the cart line sell price:

Message	Circumstance
`CartItem.SellPrice<=SellableItem.SellPrice: Price={purchaseOptionPolicy.SellPrice.AsCurrency()}`	The SellableItem has a `PurchaseOptionMoneyPolicy` (indicating it can be sold in the currency desired).
`CartItem.SellPrice<=SellableItem.Variation.SellPrice: Price={purchaseOptionPolicy.SellPrice.AsCurrency()}`	The item has a variation and the variation has a `PurchaseOptionMoneyPolicy`.
`CartItem.SellPrice<=PriceCard.ActiveSnapshot: Price={purchaseOptionPolicy.SellPrice.AsCurrency ()}\|Qty={tier.Quantity}`	The SellableItem has a calculated PriceSnapshotComponent and `line.Quantity <= tier.quantity` (takes first in descending order).