releasetools: Return the actual image size when building logical partitions.

When verity is enabled, `partition_size` has the "adjusted" partition
size for holding the filesystem files (i.e. excluding verity hashtree,
and FEC metadata if applicable), whereas `original_partition_size` has
the one for the actual image returned by build_image.py.
`partition_size` must be smaller than `original_partition_size`. As a
result, the later assertion in Makefile (e.g. assert-max-image-size) may
fail to hold when using `partition_size`.

This CL addresses the issue by returning the value in
`original_partition_size` instead, if available. It also changes to
include both values when dumping the size info on image creation
failure.

Fixes: 79106666
Test: `m dist` with aosp_walleye-userdebug
Test: Set up walleye to use logical partitions, with a reserved size of
      20MiB. `m systemimage` no longer fails.
Test: Set up walleye that doesn't use verified boot. Use `m systemimage`
      to build an oversized image. Check the error message.
Change-Id: I41d77bffa85e8eadfbf4a2a7dcd2e798fadfdab7