Display static documentation information for multipart properties in OpenAPI 3.0 files

Following on from https://github.com/swagger-api/swagger-ui/issues/5164, I am suggesting that for specs with multipart/form-data that we allow the main request body of the spec to show a preview of the payload, rather than leaving it blank (and appearing unrendered) like so: For "Try it now" feature it appears rendered correctly: I am proposing something similar to the above pic, even if text areas/drop-downs appear greyed out. Attached following spec as an example which highlights what I thought was an issue, but turns out to be a feature: v3.20.2_multipart_snippet.txt Cheers, Rich