.NET Workflows - Add support for tool approval

[crickman]

Motivation and Context

Support tool approval for function and mcp tools.

Description

• Introduce UserInputRequest and UserInputResponse to handle approval requests
• Rename existing request-port objects for clarity
• Verify serialization
• Update sample

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 adds support for tool approval in .NET workflows by introducing new event types that distinguish between different kinds of user input requests (messages vs. tool approvals) and separates function tool calls from general user input handling.

Key changes:

• Renamed and refactored event classes to better distinguish between user messages (UserMessageRequest/UserMessageResponse) and tool-related events (AgentFunctionToolRequest/AgentFunctionToolResponse)
• Added new UserInputRequest/UserInputResponse classes to handle tool approval scenarios for both function and MCP tools
• Updated workflow execution logic to handle separate request ports for function calling and user input approval

Reviewed Changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
Events/UserMessageRequest.cs	Replaces InputRequest with simplified user message request
Events/UserMessageResponse.cs	Renames InputResponse to UserMessageResponse
Events/UserInputRequest.cs	New class for tool approval requests
Events/UserInputResponse.cs	New class for tool approval responses
Events/AgentFunctionToolRequest.cs	Renames AgentToolRequest to clarify function-specific nature
Events/AgentFunctionToolResponse.cs	Renames AgentToolResponse to match request naming
Events/InputRequest.cs	Removed (replaced by UserMessageRequest)
Events/AgentToolRequest.cs	Removed (replaced by AgentFunctionToolRequest)
Events/AgentToolResponse.cs	Removed (replaced by AgentFunctionToolResponse)
ObjectModel/QuestionExecutor.cs	Updated to use UserMessageRequest/UserMessageResponse
ObjectModel/InvokeAzureAgentExecutor.cs	Added user input handling logic and separated function call handling
Interpreter/WorkflowActionVisitor.cs	Added separate request ports for function calling and user input
WorkflowAgentProvider.cs	Updated documentation to reference renamed classes
Microsoft.Agents.AI.Workflows.Declarative.csproj	Suppressed MEAI001 warning
Test files	Updated tests to use renamed classes and added new tests for UserInputRequest/UserInputResponse
samples/.../ExecuteWorkflow/Program.cs	Updated sample to handle new event types including tool approval