.Net Bug: IChatCompletionService produces StreamingChatMessageContent without role assignment

[crickman]

Describe the bug
AuthorRole is not assigned to each and every StreamingChatMessageContent produced

To Reproduce
Steps to reproduce the behavior:

1. Open concepts sample OpenAI_ChatCompletionStreaming.StreamTextContentAsync
2. Set breakpoint on Console.Write(chatUpdate.Content);
3. Run sample
4. Examine: chatUpdate.Role

Expected behavior
Message has Role property assigned to each StreamingChatMessageContent instance (similiar to ModelId and other properties)

Platform

• Language: C#
• Source: Main