Add a new depsgraph builder class that includes invisible objects and
use that in the Alembic exporter.
Alembic supports three options for visibility, "visible", "inherited",
and "hidden". This means that parents can be hidden and still have
visible children (contrary to USD, where invisibility is used to prune
an entire scene graph subtree). Because of this, the visibility is
stored on the transform node, as that represents the Object in Blender
and thus keeps the Alembic file as close to Blender's own structure as
possible.
Reviewed By: Sergey
Differential Revision: https://developer.blender.org/D8595
