Fix: @withVisibility decorator

[timotheeguerin]

fix #2517

[github-actions]

Changes in this PR will be published to the following url to try(check status of TypeSpec Pull Request Try It pipeline for publish status):
Playground: https://cadlplayground.z22.web.core.windows.net/prs/2544/

Website: https://tspwebsitepr.z22.web.core.windows.net/prs/2544/

[timotheeguerin]

Todo need to update the doc to explain this new behavior
Todo add tests

[mikekistler]

I think there is still a problem. I believe that any model I define in TypeSpec should appear in the OpenAPI with all the properties I defined in them (in the absence of a "withVisibility" decorator).

But this isn't the case, as this playground illustrates. The Dog model is missing the secretName property. Isn't that wrong?

[timotheeguerin]

yeah I guess, my fix might actually only really fix the other issue Brian thought about. So this remaining fix I guess is about the openapi3 emitter not using visibility for unreachable models.

So the 2 issues are:

• Unreachable models shouldn't be affected by visibility
• Model used with @withVisibility and referenced in an operation shouldn't have their visibility reapplied