Retain order of produces media types in @ExceptionHandler

[IMurzich]

Fix error when corrupt order of produces media types for @ExceptionHandler.

For example, the following returns xml by default.

@ExceptionHandler(exception = Exception.class,
    produces = {"application/json", "application/xml"})

[sbrannen]

Hi @IMurzich,

Congratulations on submitting your first PR for the Spring Framework! 👍

However, before we process this PR, we need to take care of the following.

1. Please explain the error scenario you are attempting to fix.
2. Please introduce a unit or integration test which fails before the fix and passes after the fix.

Regarding point # 1, I realize you added some text to this issue's description, but it is not fully clear to me what you mean. So, perhaps you can just expound on that.

Thanks

[IMurzich]

Hi @sbrannen,

I've added test. Please check it.

Thanks.

[IMurzich]

Purpose of change:
I have controller and exceptions handler in it. My rest service can return json or xml replies. Therefore I want to return exceptions in json or xml too. Exception handler annotated @ExceptionHandler(value=Exception.class, produces = {"application/json", "application/xml"}). And I expect to get json response with error (accept=/), but I receive xml response because HashSet doesn't keep order of produce media types and returns application/xml as first media type.