Provide access to non-standard status codes from ServerHttpResponse

[wilkinsona]

In a similar vein to #22872, it would be useful to have access to the raw status code rather than null when dealing with a response with a status code that is not known to HttpStatus.

[jhoeller]

This is available in some form (managing locally set status code values outside of the enum range) on AbstractServerHttpResponse - would a downcast be sufficient for your purposes?

Since the ServerHttpResponse interface is more about modifying than introspecting the response, I'm rather reluctant to add further introspection methods to the interface.

[wilkinsona]

Yes, that works nicely. Thanks for the suggestion.