liblp: Require block-aligned partition sizes.

DM_TABLE_LOAD will reject dm-linear entries if their size is not a
multiple of the backing device's logical block size. For example, a
partition of 10GiB+512 bytes will fail to map in device-mapper if the
logical block size is 4096 bytes. To address this, this patch adds a
few changes to liblp:

The block size given to lpmake is now recorded in LpGeometryMetadata.
The block size must be a multiple of the sector size. In addition,
partiton sizes are now aligned to the block size, and the super
partition must have enough free space to allocate at least one block (in
addition to storing metadata).

GrowPartition now has multiple checks that the block-size invariant is not
violated, to ensure that no invalid partition tables will be created.

Bug: 79173901
Test: liblp_test gtest
Change-Id: I484aac1f9b90ebd92dc1c89ce1e09cd89bbb441e