Describe the bug

Currently we will directly return the raw response for union cases in sample generation, this will exist issues when model have different serializeName and client name. I think we should handle part of unions also.

Reproduction

NA

Checklist

• Follow our Code of Conduct
• Check that this issue is about the Azure libraries for typespec. For bug in the typespec language or core libraries file it in the TypeSpec repo
• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• The provided reproduction is a minimal reproducible example of the bug.