fix: normalization regression

[shockey]

Addresses:

• UI get stuck on loading image swagger-ui#4466
• UI hangs when there are top level produces and request header reference swagger-ui#4467

[shockey]

The issue here was that $ref'd parameters were always failing the existential test in the code, which led to an infinite loop of pushing onto operation[inheritName].

• This code really should be rewritten, the current implementation feels messy. It's hard to see what's going on.
• I was surprised to find that the current tests didn't catch this. In light of that I added the example from UI hangs when there are top level produces and request header reference swagger-ui#4467 as a specific test for this bug. The normalizer is version-agnostic, so there isn't a need for a sister OAS3 test.