.NET Workflows - Support agent level function invocation for declarative workflow

[crickman]

Motivation and Context

Enable function calling for declarative workflows (when an agent within the workflow has a function tool).

Description

• An agent that defines a function will either have that function auto-executed (if available) or else a request is made to the caller via AgentToolRequest. The caller may then respond with AgentToolResponse.

• Integration tests add for both auto-execute and caller-requested modes.

• Sample updated

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull Request Overview

This PR enables function calling capabilities for declarative workflow agents, allowing agents to either auto-execute functions when available or request function execution from the caller through a tool request/response mechanism.

• Added agent-level function invocation support with auto-execute and caller-requested modes
• Implemented new tool request/response event system for function calls
• Added comprehensive integration tests for both execution modes

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
ToolInputWorkflowTest.cs	New integration test class validating both auto-invoke and request-invoke function execution modes
FunctionTool.yaml	Test workflow configuration that invokes agents with function tools multiple times
MenuPlugin.cs	Test plugin providing menu-related functions for integration testing
ToolAgent.yaml	Agent configuration defining menu-related function tools
InvokeAzureAgentExecutor.cs	Enhanced executor to handle function calls and tool request/response workflow
WorkflowActionVisitor.cs	Updated to support the new multi-step agent invocation pattern with tool handling
WorkflowAgentProvider.cs	Added properties for function configuration and concurrent invocation settings
AzureAgentProvider.cs	Enhanced to configure function invocation capabilities on chat client agents
AgentToolRequest.cs/AgentToolResponse.cs	New event classes for function call request/response communication
ChatMessageExtensions.cs	Added extension method to convert function results to chat messages
WorkflowHarness.cs	Updated test harness to support tool request/response scenarios and improved logging
IntegrationTest.cs	Modified to accept function tools for agent configuration
AgentFactory.cs	Added new tool agent configuration and menu plugin registration

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