[WIP] Start Agentic Support

[rido-min]

This pull request introduces a new AgenticIdentity model to support agent-specific authentication throughout the Teams API client libraries. It refactors authentication and client classes to consistently pass agentic identity information, updates method signatures, and improves extensibility for agent-based scenarios.

Agentic Identity Integration

• Added the AgenticIdentity class to represent agent-specific authentication properties and a static method to construct it from a properties dictionary.
• Updated IHttpCredentials and related implementations (ClientCredentials, TokenCredentials) to accept and utilize AgenticIdentity for resolving tokens, including changes to delegate signatures and method parameters. [1] [2] [3] [4]

API Client and Bot Client Refactoring

• Refactored constructors for ApiClient, BotClient, BotTokenClient, and BotSignInClient to accept a scope parameter and propagate agentic identity information through client instantiation. [1] [2] [3] [4]
• Updated client methods to pass AgenticIdentity when sending HTTP requests, ensuring agent context is included in all relevant API calls. [1] [2] [3] [4] [5]

Token and Response Handling

• Introduced the ITokenResponse interface for token responses and updated TokenResponse to implement it, improving consistency and extensibility of token handling.

Miscellaneous Improvements

• Added [JsonExtensionData] to the Account.Properties property to support dynamic extension data in serialization.
• Minor code cleanup and organization, including using directives and commented-out legacy constructors. [1] [2]

These changes collectively enable agent-specific authentication flows and prepare the codebase for advanced agentic scenarios in Teams API integrations.