Add code samples for the "using tools" page (#698)

Author: justinyoo

docs/guides/tools/responses/file_search.cs

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+// SAMPLE: Get information from file search through Responses API
+// PAGE: https://platform.openai.com/docs/guides/tools?tool-type=file-search
+// GUIDANCE: Instructions to run this code: https://aka.ms/oai/net/start
+#pragma warning disable OPENAI001
+
+#:package OpenAI@2.*
+#:property PublishAot=false
+
+using OpenAI.Responses;
+
+string key = Environment.GetEnvironmentVariable("OPENAI_API_KEY")!;
+OpenAIResponseClient client = new(model: "gpt-5", apiKey: key);
+
+ResponseCreationOptions options = new();
+options.Tools.Add(ResponseTool.CreateFileSearchTool([ "<vector_store_id>" ]));
+
+OpenAIResponse response = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("What is deep research by OpenAI?")
+    ])
+], options);
+
+Console.WriteLine(response.GetOutputText());

docs/guides/tools/responses/function_calling.cs

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+// SAMPLE: Generate response from function calling through Responses API
+// PAGE: https://platform.openai.com/docs/guides/tools?tool-type=function-calling
+// GUIDANCE: Instructions to run this code: https://aka.ms/oai/net/start
+#pragma warning disable OPENAI001
+
+#:package OpenAI@2.*
+#:property PublishAot=false
+
+using System.Text.Json;
+using OpenAI.Responses;
+
+string key = Environment.GetEnvironmentVariable("OPENAI_API_KEY")!;
+OpenAIResponseClient client = new(model: "gpt-5", apiKey: key);
+
+ResponseCreationOptions options = new();
+options.Tools.Add(ResponseTool.CreateFunctionTool(
+        functionName: "get_weather",
+        functionDescription: "Get current temperature for a given location.",
+        functionParameters: BinaryData.FromObjectAsJson(new
+        {
+            type = "object",
+            properties = new
+            {
+                location = new
+                {
+                    type = "string",
+                    description = "City and country e.g. Bogotá, Colombia",
+                }
+            },
+            required = new[] { "location" },
+            additionalProperties = false
+        }),
+        strictModeEnabled: true
+    )
+);
+
+OpenAIResponse response = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("What is the weather like in Paris today?")
+    ])
+], options);
+
+Console.WriteLine(JsonSerializer.Serialize(response.OutputItems[0]));

docs/guides/tools/responses/remote_mcp.cs

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+// SAMPLE: Generate response from remote MCP through Responses API
+// PAGE: https://platform.openai.com/docs/guides/tools?tool-type=remote-mcp
+// GUIDANCE: Instructions to run this code: https://aka.ms/oai/net/start
+#pragma warning disable OPENAI001
+
+#:package OpenAI@2.*
+#:property PublishAot=false
+
+using OpenAI.Responses;
+
+string key = Environment.GetEnvironmentVariable("OPENAI_API_KEY")!;
+OpenAIResponseClient client = new(model: "gpt-5", apiKey: key);
+
+ResponseCreationOptions options = new();
+options.Tools.Add(ResponseTool.CreateMcpTool(
+    serverLabel: "dmcp",
+    serverUri: new Uri("https://dmcp-server.deno.dev/sse"),
+    toolCallApprovalPolicy: new McpToolCallApprovalPolicy(GlobalMcpToolCallApprovalPolicy.NeverRequireApproval)
+));
+
+OpenAIResponse response = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("Roll 2d4+1")
+    ])
+], options);
+
+Console.WriteLine(response.GetOutputText());

docs/guides/tools/responses/web_search.cs

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+// SAMPLE: Get information from web search through Responses API
+// PAGE: https://platform.openai.com/docs/guides/tools?tool-type=web-search
+// GUIDANCE: Instructions to run this code: https://aka.ms/oai/net/start
+#pragma warning disable OPENAI001
+
+#:package OpenAI@2.*
+#:property PublishAot=false
+
+using OpenAI.Responses;
+
+string key = Environment.GetEnvironmentVariable("OPENAI_API_KEY")!;
+OpenAIResponseClient client = new(model: "gpt-5", apiKey: key);
+
+ResponseCreationOptions options = new();
+options.Tools.Add(ResponseTool.CreateWebSearchTool());
+
+OpenAIResponse response = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart(
+            "What was a positive news story from today?"
+        )
+    ])
+], options);
+
+Console.WriteLine(response.GetOutputText());