.NET MEAI - Translation from `ResponseItem to `ChatMessage` / `AIContent` dropping `ResponseContentPart` with file url or content.

[crickman]

Repro PR

Note: Supporting this requires:

1. Fix to Open AI SDK
   PR: Expose ResponseContentPart.InputImageUrl openai/openai-dotnet#874
   ISSUE: [BUG] ImageUrl not exposed on ResponseContentPart for CreateInputImagePart openai/openai-dotnet#875
2. Subsequent update to MEAI
3. Integration of both fixes and validation in AF integration tests

Public URI

        ResponseItem messageItem =
            ResponseItem.CreateUserMessageItem(
                [
                    ResponseContentPart.CreateInputTextPart("Test message"),
                    ResponseContentPart.CreateInputImagePart(new Uri("https://example.com/image.png")),
                ]);

        IEnumerable<ResponseItem> messageItems = [messageItem];

        var chatMessages = messageItems.AsChatMessages();
        ChatMessage chatMessage = Assert.Single(chatMessages);
        Assert.Equal(ChatRole.User, chatMessage.Role);
        Assert.Equal(2, chatMessage.Contents.Count); // <<< FAILS HERE
        TextContent textContent = Assert.IsType<TextContent>(chatMessage.Contents[0]);
        Assert.Equal("Test message", textContent.Text);
        UriContent uriContent = Assert.IsType<UriContent>(chatMessage.Contents[1]);
        Assert.Equal("https://example.com/image.png", uriContent.Uri.ToString());

Content URI (Base64)

        ResponseItem messageItem =
            ResponseItem.CreateUserMessageItem(
                [
                    ResponseContentPart.CreateInputTextPart("Test message"),
                    ResponseContentPart.CreateInputImagePart(BinaryData.FromBytes(Encoding.UTF8.GetBytes("image data")), "image/png"),
                ]);

        IEnumerable<ResponseItem> messageItems = [messageItem];

        var chatMessages = messageItems.AsChatMessages();
        ChatMessage chatMessage = Assert.Single(chatMessages);
        Assert.Equal(ChatRole.User, chatMessage.Role);
        Assert.Equal(2, chatMessage.Contents.Count); // <<< FAILS HERE
        TextContent textContent = Assert.IsType<TextContent>(chatMessage.Contents[0]);
        Assert.Equal("Test message", textContent.Text);
        UriContent uriContent = Assert.IsType<UriContent>(chatMessage.Contents[1]);
        Assert.Equal($"data:image/png;base64,{Convert.ToBase64String(Encoding.UTF8.GetBytes("image data"))}", uriContent.Uri.ToString());

[stephentoub]

Repro? What is this referring to?

[crickman]

@stephentoub , I've provided repro-steps in the description and as a PR with two failing tests. As noted, there's an underlying issue with the OpenAI SDK that must be addressed prior to updating MEAI (or else use Reflection, if that's valid.)

string? imageUrlValue = imageUrlPart.GetType().GetProperty("ImageUrl")!.GetValue(imageUrlPart) as string;

dotnet/extensions#7176