fs_mgr: Add a library for managing logical partitions.

This library has methods to build, read, and modify logical partition tables
based on device-mapper targets. Targets currently supported are
dm-linear and dm-zero.

Note: this is a revert of a revert, with changes to fix Mac build
bustage.

Bug: 79173901
Test: N/A
Change-Id: If89a788d1919ce8ddc6eedaecc9687a92f111dfa