Merge "libsnapshot: Fetch device size from header" into main am: 7428705371

Original change: https://android-review.googlesource.com/c/platform/system/core/+/2974622

Change-Id: I42f1f048d6a8298c8cb82f7f3eef710998598743
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>