Allow Jetedge to build abstract objects

Jetedge fails anytime the build path contains an abstract class. Create a new method that allows for the user to specify a particular child to be used in place of abstract class, or allows Jetedge to create a proxy that will be have its fields populated.

Start by tracing Jetedge's build path to identify where abstract classes cause construction to fail. Define how callers select a concrete child or request a proxy whose fields are populated, then verify that build paths containing abstract classes complete successfully.

Written by the indexing model from the issue text.