This change adds support for transforming a property set after its
contents. This allows a transform to recursively prune empty property
sets that were created for a module.
The transformPropertySet method was renamed to
transformPropertySetBeforeContents and a new
transformPropertySetAfterContents method was added.
Bug: 148933848
Test: m nothing
Change-Id: Ia198d47e042b98c69406db4bc12859869816a387
Returning nil from transformPropertySet in order to remove it did
not work because it ends up comparing as (*bpPropertySet, nil) and
not an untyped nil which causes the test against nil to fail.
This change adds tests to check that returning nil will delete a
property/property set from the containing property set and fixes the
code so that it passes the tests. It extracts common code to transform
a property set and its contents as well as code for creating new
property sets.
Bug: 148933848
Test: m nothing
Change-Id: I35dc3c39c76e701821891622615c09b094cf697f
