IChatCompletion Multiple Results / New Interfaces

[rogerbarreto]

Motivation and Context

Add potential for IChatCompletion with multiple results per prompt.

Description

• Adds new Interfaces/Abstractions for Chat Results: IChatResult, IChatStreamingResult, IChatMessage
• Adds new IChatCompletion interface methods for Streaming and Non-Streaming results
• Moves old IChatCompletion interface methods IAsyncEnumerable<string> GenerateMessageStreamAsync and Task<string> GenerateMessageAsync as extensions for retro compatibility
• Changed ChatAsText to use the new multiple results implementations
• Makes ChatHistory.ChatMessage & ChatHistory.AuthorsRole types obsolete (discouraging usage of those implementation in favor of new IChatMessage
• ChatHistory abstraction now extends from List<IChatMessage>
• Updates all Samples using the new interfaces.

Paves the way to ... (Futures)

• Remove ChatHistory.ChatMessage inner class
• Remove ChatHistory.AuthorsRole enums
• Make ChatHistory an abstract class or an IChatHistory interface.
• Rename ITextCompletionResult to ITextResult
• Rename ITextCompletionStreamingResult to ITextStreamingResult

Contribution Checklist

• [x] The code builds clean without any errors or warnings
• [x] The PR follows SK Contribution Guidelines (https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
• [x] The code follows the .NET coding conventions (https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions) verified with dotnet format
• [x] All unit tests pass, and I have added new tests where possible
• [x] I didn't break anyone :smile:

[stephentoub]

Moves old IChatCompletion interface methods IAsyncEnumerable GenerateMessageStreamAsync and Task GenerateMessageAsync as extensions for retro compatibility

What's our plan for tracking / removing such temporary measures? Do we actually need them?

[rogerbarreto]

What's our plan for tracking / removing such temporary measures? Do we actually need them?

@stephentoub The plan here is to keep those as extensions while we still use it as part of the SK internal implementations.

Once we moved all the SK implementations to use the Result approach those extension methods will be moved to another package/namespace Extensions or flagged as Obsolete.