For the same message type, code gen only picks up the handler in saga, but not in a separate subscriber

[taizoon-repeatmd]

Describe the bug
For the same message type, code gen only picks up the handler in saga, but not in a separate subscriber

To reproduce:

• Have a single message type that is handled by a Saga and also handled by a completely separate non-saga handler
• The system uses the MultipleHandlerBehavior.Separated setting

What's happening is that Wolverine is correctly generating the code for the Saga handler, but not generating a file for the non-saga handler. I suspect the problem is in the HandlerGraph implementation of ICodeFileCollection not returning the right "sticky" handlers