4019 [image_picker] Fix rotation when camera is a source (cla: yes, p: image_picker, platform-ios)

4027 [in_app_purchase] Avoid nullable Future.value (cla: yes, p: in_app_purchase, platform-ios)

4035 [in_app_purchase] Only register transactionObservers when someone is listening to purchaseUpdates (cla: yes, p: in_app_purchase, platform-ios)