Replaced "MIME media type" with the recommended terminology: "media type"

[csarven]

This PR is a class 2 change updating the following documents:

• Activity Streams 2.0 (uses "media type", references IANA-MEDIA-TYPES. updates changelog)
• Activity Vocabulary (uses "media type", references IANA-MEDIA-TYPES, clarifies range, updates changelog)
• ActivityStreams 2.0 Terms (clarifies range)
• Activity Streams 2.0 ontology (uses "media type", references IANA-MEDIA-TYPES)

[nightpool]

"MIME type" is the way the media type is most commonly referred to, and the name that is most recognizable to developers, so I wonder if maybe we should retain it as a parenthetical in some cases e.g. in the first reference say something like media type (aka MIME type)

[csarven]

I don't have data on which term is most recognizable. However, "media type" has been recommended by IANA for about three decades. I suspect developers are familiar with both terms, and I also believe that developers from the mid-90s onward, as well as those implementing these specifications, would be fine with using just "media type". In the first instance, I've included a reference that I think should suffice: "media type ([IANA-MEDIA-TYPES])".

[nightpool]

Just to pick a different server-side ecosystem at random, in Ruby, the main library most developers use is called Mime::Type, and the Rails docs refer to "MIME content-type" when explaining how to set a custom Content-Type header: https://guides.rubyonrails.org/layouts_and_rendering.html#the-content-type-option. So I think we have good evidence that the term is still very widespread. I think having an "aka" or "formerly known as" clarifier the first time the term is used is a very small ask that would help improve the experience of implementers significantly.

[csarven]

ActivityPub doesn't use "MIME", yet that worked out fine with the developers?