Proposal: add support for `querystring` Parameter Format

[DmitryAnansky]

OpenAPI 3.2.0 introduced a new parameter location, querystring, described in
Extending Support for Querystring Formats,
along with several additional constraints:

• query — Parameters appended to the URL. For example, in /items?id=###, the id parameter is a query parameter.
  It MUST NOT appear in the same operation (or in the operation’s path item) as an in: "querystring" parameter.

• querystring — A parameter that treats the entire URL query string as a single value. It MUST be specified using the content field, most commonly with the media type application/x-www-form-urlencoded, using Encoding Objects in the same way as request bodies of that media type.
  It MUST NOT appear more than once, and MUST NOT appear in the same operation (or in the operation’s path item) as any in: "query" parameters.

Arazzo could consider supporting this parameter directly, or alternatively document a recommended approach, so that tooling can consistently determine how to handle this syntax.

[handrews]

Note that the content: {application/x-www-form-urlencoded: {...}} field in an in: querystring parameter Object works exactly like the same structure in a Request Body Object or Response Object. So if Arazzo can handle those Objects, it should be able to handle in: querystring Parameter Objects.