Parameters on Path Item Object are ignored

[gweis]

OpenAPI 3 allows for parameter definition directly on a Path Item object. These parameters should be applicable to all operations under this path. However, the way validation works here is that only parameters defined on an 'Operation object' are considered for validation.

I have created a few simple test cases https://github.com/gweis/openapi-core/commit/787799081db01f9b7ebe491e886e947dd270bfc2 to demonstrate the issue (happy to turn them into a pull request).
If my understanding of the spec is correct, all these tests should succeed, but currently they fail. i.e. parameter resId is not validated, not seen as missing, or not even parsed and returned.

[gweis]

Related to Pylons/pyramid_openapi3#25