Calling android.NewContext() in tests results in a context that
contains all the mutators, module types, and singletons, which
causes unexpected interactions in unit tests. Create an empty
context instead, and add in only the necessary mutators, module
types, and singletons.
Bug: 36366816
Test: soong tests
Change-Id: Ic61262c37e3436b3ad4ccaca18b737021c304be6
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
