Make MEDI implemention registrations idempotent

[JMolenkamp]

Proposed Changes

• Make MEDI implementation registrations in AutofacRegistration.Populate calls idempotent. Allowing for multiple calls to Populate without duplicating registrations and callback.

[tillig]

Is this a problem you've run into that you're trying to solve? The PR explains what was changed, but the why is more important. This package has been out for years and we've had no issue reports about this; and adding it now is a potential breaking behavior change.

[JMolenkamp]

No, it's more of a correctness thing that I stumbled upon. I can't really see how this would become a breaking change, but obviously I can't foresee every usage.

[tillig]

I see what you're saying, and I think you're generally right. I can just never be sure what stuff people start counting on, even if it seems like it's not something to be counted on. One person's 0.0.1 bug fix is another's 1.0.0 "why did you break my app?" behavior change sometimes. Let me think about it a bit. I lean toward the correctness side, just want to be cautious about "if it ain't broke, don't fix it."

[JMolenkamp]

Understandable, easy for me to say from where I'm standing.