[refactor]: dump `InputOperation.RequestBodyMediaType`

[archerzz]

Clear and concise description of the problem

This was found during investigation of #4208. We have two properties regarding request body media type in InputOperation:

• RequestBodyMediaType: It's determined by the request body parameter type
  

  typespec/packages/http-client-csharp/emitter/src/lib/operation-converter.ts

  Line 92 in 2d4f55f

  RequestBodyMediaType: getBodyMediaType(method.operation.bodyParam?.type),

  • It's not used in MGC.
  • In autorest.csharp, it's used by CmcRestClientBuilder and RestClientBuilder
• RequestMediaTypes: it's determined by scanning the operation, which I think is more accurate
  

  typespec/packages/http-client-csharp/emitter/src/lib/operation-converter.ts

  Line 96 in 2d4f55f

  RequestMediaTypes: getRequestMediaTypes(method.operation),

  • It's not used in MGC either (probably MGC hasn't implement the various media type support?)
  • In autoest.csharp: it's used by OperationMethodChainBuilder when setting the request Content-Type header: https://github.com/Azure/autorest.csharp/blob/a19bafb7ff7418930deb75b1df40ccbf55825228/src/AutoRest.CSharp/LowLevel/Output/OperationMethodChainBuilder.cs#L557
  • it's used by ConvenienceMethod when determine how to serialize the input body: https://github.com/Azure/autorest.csharp/blob/a19bafb7ff7418930deb75b1df40ccbf55825228/src/AutoRest.CSharp/LowLevel/Output/ConvenienceMethod.cs#L36

When we implement MGC regarding media types, we should use RequestMediaTypes for all kinds of SDKs (DPG, MPG, HLC,...).

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[JoshLove-msft]

@archerzz assigning this to you as you are working on the e2e story for the media types.

[JoshLove-msft]

Need to figure out why there are two properties. Also, this may not necessarily just be out requests. We need an inventory of what the request content-type properties and response content-types are. It's not clear what value having the response content-type be parameterizable via Accept header. For requests, then we could parameterize into 1 method with a contentType parameter.

public FooOperation(FooModel foo, string contentType)

But maybe we don't even need the contentType parameter as customers can always use protocol methods for this. If we don't include the contentType, then the client library would choose a content type, prioritizing JSON and then binary. Else just choose the first one.