simplification allows us to settle on a single interface,
graphNodeExpandsInstances for all types if instance expanders. The only
other specific class of resource we need to detect during pruning is the
nodeExpandApplyableResource node, which is already classified under the
GraphNodeResourceInstance interface.
create interfaces that nodes can implement to declare whether they
expand into instances of some sort, using the instances.Expander, and/or
whether use the instances.Expander to find instances.
included is a rough transformer implementation to remove these nodes
from the apply graph.
