MeidaType's subtype with suffix should be a subset of a subtype without suffix

[kichalla]

According to https://tools.ietf.org/html/rfc6839#section-2, content like application/problem+json should be able to be processed as though its application\json too, but currently we don't consider application/problem+json as a subtype of application\json.

Related issue: aspnet/Mvc#8156

[kichalla]

cc @Tratcher

[Eilon]

Tagging @dougbu and @jkotalik who I think both have a great deal of knowledge on this matter.

[dougbu]

@kichalla and I discussed this, reviewed the spec(s), and I agree it's a bug.