[SK2] send unsynced attributes when syncing purchases (#4245)

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### Checklist
- [x] If applicable, unit tests
- [ ] If applicable, create follow-up issues for `purchases-android` and
hybrids

### Motivation
When calling syncPurchases with StoreKit 2, we aren't including any
unsynced subscriber attributes.

### Description
This PR modifies the StoreKit 2 syncPurchases network request to include
unsynced subscriber attributes, the storefront, and a nil
`presentedOfferingContext`.

---------

Co-authored-by: Will Taylor <wtaylor151@gmail.com>

Sources/Purchasing/Purchases/PurchasesOrchestrator.swift

@@ -1139,11 +1139,19 @@ private extension PurchasesOrchestrator {
                         return
                     }
 
+                    let transactionData: PurchasedTransactionData = .init(
+                        appUserID: currentAppUserID,
+                        presentedOfferingContext: nil,
+                        unsyncedAttributes: unsyncedAttributes,
+                        source: .init(
+                            isRestore: isRestore,
+                            initiationSource: initiationSource
+                        )
+                    )
+
                     self.backend.post(receipt: .empty,
                                       productData: nil,
-                                      transactionData: .init(appUserID: currentAppUserID,
-                                                             source: .init(isRestore: isRestore,
-                                                                           initiationSource: initiationSource)),
+                                      transactionData: transactionData,
                                       observerMode: self.observerMode,
                                       appTransaction: appTransactionJWS) { result in
 

Tests/StoreKitUnitTests/PurchasesOrchestratorSK2Tests.swift

@@ -578,6 +578,8 @@ class PurchasesOrchestratorSK2Tests: BasePurchasesOrchestratorTests, PurchasesOr
 
         expect(self.backend.invokedPostReceiptData).to(beTrue())
         expect(self.backend.invokedPostReceiptDataParameters?.data) == .jws(transaction.jwsRepresentation!)
+        expect(self.backend.invokedPostReceiptDataParameters?.transactionData.unsyncedAttributes).toNot(beNil())
+        expect(self.backend.invokedPostReceiptDataParameters?.transactionData.presentedOfferingContext).to(beNil())
         expect(customerInfo) == mockCustomerInfo
     }