Allow Parameter/Header examples w/content

Parameter and Header serialization is complex, particularly when
using the `content` field to use a Media Type Object.

In such scenarios, the serialization occurs in two steps:
The first step is to serialize the data to the media type, which
can be captured by the `examples` field of the Media Type Object.

The second is the encoding/escaping of the media type document
for use in a URI, HTTP header, or other location with its own rules.

Sometimes the part needing illustration with an example is at one
level, sometimes at another, and sometimes it is helpful to show
both.

For simplicity, the "data" examples are always treated as the
overall input data, so they would be the same at both levels.
This is also because it is not always possible to show each step,
particularly when there are binary serializations. This allows
showing either step (or both steps) with both data and serialization,
depending on what makes sense for the use case.