fix: change commons MLKit product from BarcodeScanning to ObjectDetection with explanatory comment

Author: arrrrny

packages/google_mlkit_barcode_scanning/ios/google_mlkit_barcode_scanning/Package.resolved

@@ -22,7 +22,15 @@ let package = Package(
         .target(
             name: "google_mlkit_commons",
             dependencies: [
-                .product(name: "MLKitBarcodeScanning", package: "google-mlkit-swiftpm")
+                // google-mlkit-swiftpm does not expose standalone MLKitVision or MLKitCommon
+                // library products — they are only available as binary targets bundled inside
+                // composite products (e.g. MLKitBarcodeScanning, MLKitFaceDetection, etc.).
+                // All vision-family products include MLKitVision + MLKitCommon (via the Common
+                // target), so we must pick one even though Commons itself does not use the
+                // specific module. MLKitObjectDetection is used here as a generic choice; the
+                // unused xcframework has no material impact because any real app using Google
+                // ML Kit will depend on at least one vision plugin that already brings it in.
+                .product(name: "MLKitObjectDetection", package: "google-mlkit-swiftpm")
             ],
             path: "Sources/google_mlkit_commons"
         )