* Update M.A.AI.OpenAI implementations
- There was only a ChatClient-based agent. Add a Responses one, too.
- Fix the public extension methods to create OpenAI types even when not backed by the right OpenAI client.
- Add reusable AgentRunResponse{Update} to ChatResponse{Update} conversion routines that are then used by the OpenAI agents and elsewhere
* Address feedback
* Make serialize methods sync and rename one to match others.
* Remove unnecessary async postfixes.
* Remove nullability of ChatMessageStore.Serialize return type, since the default JsonElement already represents an undefined json element.
* Fix unit test
* Rename AI Agent packages to use Microsoft.Agents.AI
* Fix for build
* Fix formatting
* Fix formatting
* Ignore in VSTHRD200 in migration samples
* Ignore in VSTHRD200 in migration samples
* Add some missing projects and run format
* Fix build errors
* Address code review feedback
* Fix merge issues
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Co-authored-by: Mark Wallace <markwallace@microsoft.com>