Move HTTP::Multipart and HTTP::Formdata to MIME namespace

[straight-shoota]

The multipart message format is part of the MIME standard and used by a variaty of applications, not just HTTP. I suggest to rename the HTTP::Multipart type to MIME::Multipart (the MIME namespace has been added in #5765).

Similarly, HTTP::Formdata as an implementation of multipart/formdata should also be renamed to MIME::Formdata.

[RX14]

formdata is an HTTP spec, multipart is a MIME (originally used in email) spec.

formdata originally started out as https://tools.ietf.org/html/rfc1867, as HTTP specific

multipart started out in https://tools.ietf.org/html/rfc1341#page-29, as a MIME spec (MIME was originally email specific)

[straight-shoota]

More recent RFCs for multipart/formdata are https://tools.ietf.org/html/rfc2388 and https://tools.ietf.org/html/rfc7578 and they specifically state that it "can be used by a wide variety of applications and transported by a wide variety of protocols". It's not specific to HTTP (although it started with HTTP/HTML and that's the most prominent use case).

[RX14]

It should stay in http.

[straight-shoota]

So MIME::Multipart and HTTP::Formdata?

[RX14]

Yep.

[Indribell]

This can be closed. See #7085