libsnapshot: Add a tool for estimating non-A/B OTA sizes with the new COW format.

This tool allows users to estimate the COW size for a non-A/B update.
It works by scanning the partitions of two target-files packages, and
identifying moved or copied blocks, and simulating the impact in the new
COW format.

It has two modes:

    estimate_cow_from_non_ab_ota -ota_tf <path>

Will estimate the COW size for a full OTA. For an incremental OTA, you
need two target files packages:

    estimate_cow_from_non_ab_ota -source_tf <path> -ota_tf <path>

There is an optional -compression argument which accepts either "none"
or "gz".

Bug: 161497962
Test: manual test
Change-Id: I335059cd870a464f34c5d644eefefdc76775386e