Convert CowOperationType into strongly typed enums am: c6be9171dc

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2850925

Change-Id: Iaec7261920d12716a48179ab5b52d61368057e11
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>