Simplify StreamSerializationModelTemplate

[alzimmermsft]

Cleans up a lot of code in StreamSerializationModelTemplate by using an instance class to generate code. This removes the need to pass many parameters all over the place.

There is also a fix to generating fields in ModelTemplate by having the overload of getFieldProperties check if fromJsonShared can be used to determine whether the subclass should shade fields of a super class. The only time shading shouldn't happen with polymorphic types is when fromJsonShared can be used as those properties will be deserialized by the super type's fromJsonShared method, meaning the subtype doesn't need to shade.

[weidongxu-microsoft]

test https://dev.azure.com/azure-sdk/internal/_build/results?buildId=4067144&view=results
Azure/azure-sdk-for-java#41571

• polymorphic in Jackson seems not valid (@JsonTypeId no longer exist) https://github.com/Azure/azure-sdk-for-java/pull/41571/files#diff-76e958a274e00c3938d8b8d79ac1dcb08fe0e828e8bb6d3607a2e48a03d9d4f8
  
  Are we discarding Jackson right now?
• there is 4 test error in azure-ai-openai, cause appears to be the role is removed in ChatRequestUserMessage https://github.com/Azure/azure-sdk-for-java/pull/41571/files#diff-a9737ddb8c1990ceabca54a2823a384847200252da2fd5ed4c9befe6f3bfd0a8 (this may correlate with the overload of discriminator property in subclass)

[haolingdong-msft]

Hi @alzimmermsft, I merged your pr with main branch to a feature branch, and tried to regenerate for TypeSpec SDKs based on the branch. I found API view diff like below, @override is removed from getKind() in subclass. I suppose after setting share-jsonserializable-code to false, there shoud be no diff. It seems a bug. Could u please check?

PR: Azure/azure-sdk-for-java#41617
diff example: https://github.com/Azure/azure-sdk-for-java/pull/41617/files#diff-90b30f05da823f3aaaf96caa3a6234d229c84b3e93c10224183857a36a9c3b02L63
autorest.java feature branch： https://github.com/Azure/autorest.java/tree/stream-style-fix-and-sdkpackage/typespec-extension

Thanks.