libsnapshot: Verify the ordering of COW operations.

Sequence op should contain all ordered ops followed
by Replace and Zero ops. There shouldn't be any non-ordered
ops embedded between ordered ops in the sequence ordering.

Bug: 290159346
Test: inspect_cow <cow_file>, OTA
Change-Id: Ia840340b0e4be07525f216838043bf0265f690c3
Signed-off-by: Akilesh Kailash <akailash@google.com>