liburing_cpp: Add wrapper API for PrepReadFixed() am: dc84c2552b

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3534879

Change-Id: Ieafe3ba1586a327d025fbd02840496dbdcdd8e18
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>