Support passing tuple through bytes type that are meant for multipart form-data

[lmazuel]

Assuming this TypeSpec:

op uploadImage(@header contentType: "multipart/form-data", @body image: MultiPartRequest): void;

model MultiPartRequest {
  profileImage: bytes;  // This is a file. Implies filename and content-type.

  pictures: bytes[]; // This is as many part as necessary. Implies filename and content-type.
  
}

We should be able to pass tuple syntax, as supported by azure-ccore in Azure/azure-sdk-for-python#32566

For instance:

client.uploadImage(
  MultiPartRequest(
    profileImage=open("profile.jpg"),
    pictures=[
      open("pic1.jpg"), # Only the bytes
      ("specialpic.gif", open("pic4.gif")), # Bytes and filename
      ("coolpic.tiff", open("pic3.tiff"), "application/tiff"), # Bytes, filename and content-type
    ]
  )    
)

I would expect codegen just pass through the data directly to azure-core, I see not reason why codegen would update the tuple.

[iscai-msft]

Related core pr: Azure/azure-sdk-for-python#33948