- our context builder did not properly map contexts nor did it
honor the isCompilingContexts flag - required for UseBuilder
- the Editor stuff is ugly but we only need it to make the
AbstractUseBuilder happy so inline it for now and mark for deletion
once I have more time
- similarily we need to pass around the AstNode <-> Context mapping
for the UseBuilder manually for now, that should be cleaned up
and be put into the ParseSession.