Fix(medusa): Swaps in tax inclusive regions (#2557)

**What**
- Ensure that swaps can be created for orders with discounts in tax inclusive regions

**How**
- Retrieve cart with discounts and region before creating adjustments for line items in cart. 
  - In `discountService.calculateDiscountForLineItem` we used the method `totalsService.getLineItemTotals` if a line-item is tax inclusive. This method uses some fields from the cart that aren't populated on cart creation (such a `items` which caused the original error).

**Testing**
- add integration test `swaps > tax inclusive > "Complete swap flow with discount"` that creates a swap in the following environment
  - tax inclusive region 
  - tax inclusive line item to be swapped
  - fixed type discount with allocation: total

Fixes CORE-748

integration-tests/api/factories/simple-product-variant-factory.ts

@@ -14,7 +14,7 @@ export type ProductVariantFactoryData = {
   inventory_quantity?: number
   title?: string
   options?: { option_id: string; value: string }[]
-  prices?: { currency: string; amount: number }[]
+  prices?: { currency: string; amount: number, region_id?: string }[]
 }
 
 export const simpleProductVariantFactory = async (
@@ -32,7 +32,7 @@ export const simpleProductVariantFactory = async (
   const toSave = manager.create(ProductVariant, {
     id,
     product_id: data.product_id,
-    sku: data.sku ?? null,
+    sku: data.sku ,
     inventory_quantity:
       typeof data.inventory_quantity !== "undefined"
         ? data.inventory_quantity
@@ -59,6 +59,7 @@ export const simpleProductVariantFactory = async (
       variant_id: id,
       currency_code: p.currency,
       amount: p.amount,
+      region_id: p.region_id ,
     })
   }