Added Chat tool calls sample

docs/guides/text/chat/chat_tools.cs

@@ -0,0 +1,65 @@
+// SAMPLE: Generate text from a simple prompt
+// GUIDANCE: Instructions to run this code: https://aka.ms/oai/net/start 
+#:package [email protected].*-*
+#:property PublishAot=false
+
+using OpenAI.Chat; 
+
+string key = Environment.GetEnvironmentVariable("OPENAI_API_KEY")!;
+ChatClient client = new("gpt-4.1", key);
+
+ChatCompletionOptions options = new();
+options.Tools.Add(ChatTool.CreateFunctionTool(
+    functionName: nameof(MyTools.GetCurrentTime),
+    functionDescription: "Get the current time in HH:mm format",
+    functionParameters: BinaryData.FromObjectAsJson(new
+    {
+        type = "object",
+        properties = new 
+        {
+            utc = new
+            {
+                type = "boolean",
+                description = "If true, return the time in UTC. If false, return the local time."
+            }
+        },
+        required = new object[0]
+    })
+));
+
+List<ChatMessage> messages = [
+    ChatMessage.CreateUserMessage("what is the current local time?")
+];
+
+complete:
+ChatCompletion completion = client.CompleteChat(messages, options);
+messages.AddRange(ChatMessage.CreateAssistantMessage(completion));
+switch(completion.FinishReason)
+{
+    case ChatFinishReason.ToolCalls:
+        Console.WriteLine($"{completion.ToolCalls.Count} tool call[s] detected.");
+        foreach (ChatToolCall toolCall in completion.ToolCalls)
+        {
+            if (toolCall.FunctionName == nameof(MyTools.GetCurrentTime))
+            {
+                string result = MyTools.GetCurrentTime();
+                messages.Add(ChatMessage.CreateToolMessage(toolCall.Id, result));
+            }
+            else
+            {
+                Console.WriteLine($"Unknown tool call: {toolCall.FunctionName}");
+            }
+        }
+        goto complete;
+    case ChatFinishReason.Stop:
+        Console.WriteLine(completion.Content[0].Text);
+        return;
+    default:
+        Console.WriteLine("Unexpected finish reason: " + completion.FinishReason);
+        return;
+}
+
+public static class MyTools
+{
+    public static string GetCurrentTime(bool utc = false) => utc ? DateTime.UtcNow.ToString("HH:mm") : DateTime.Now.ToString("HH:mm");
+}