* When the media-type is changed, there is a new `onChangeMediaType` method to handle actions.
* If target schema properties key/value pairs does NOT equals current schema properties, clear the requestBodyValue, try-it-out request/response and validation params.
* If target schema properties key/value pairs DOES equals current schema properties, do not change or re-render schema properties
* oas3Selector `validateShallowRequired` now also validates required keys against target media-type
Fixes#6201, #6250, #6476
fixes#5181
* application/json
* application/xml
* application/x-www-form-urlencoded
* Set requestBodyValue values to be an immutable Map, as "value". Previously stored as a normal String.
* This enables adding "errors" to the Map, for validation use
* note: getOAS3RequiredRequestBodyContentType requires state.spec,
* which is not available to state.oas3
