[pm/build] prepare for out-of-build repo construct

The package build tool now produces a JSON manifest as an output format that
is usable as a complete input specification for a publish operation. The
expand tool also produces this manifest. The build passes this to the new
publish operation to perform all publishing.

Test: publish tests are backfilled later in patch series
Change-Id: Ifae5a70d07143a86ec19b1c68a8625151db2eb71