Allow tests to specify a data property that lists files or filegroup
modules that will be packaged alongside the test. Also add a path
property to filegroup modules to allow shifting the path of the
packaged files, and add ExpandSourcesSubDir to expand the filegroup
sources while including a shifted relative path in the Paths objects.
Test: soong tests, manually adding data to a module
Change-Id: I52a48942660e12755d313ef13279313361b4fc35