.Net: SK integration with MEAI Abstractions - #10754

…nts) Phase 1 (#10651)

### Motivation and Context

- Resolves partially #10319 

This change adds a new `IChatClientSelector` abstraction to work without
breaking current `IAIServiceSelector` implementations.

This was necessary because `Kernel` now will be able to resolve
`IChatClient`s which are not `IAIService` implementations, and
`OrderedAIServiceSelector` now can select not only `AIServices` but
`ChatClients` as well by implementing the `IChatClientSelector`
interface.

All other changes are related to test accepting `IChatClient`s added to
the `Service` DI container, ensuring they work as expected together with
current `IChatCOmpletionService` and `ITextGenerationService` in the
`Kernel`.

…nto upstream/feature-msextensions-ai

…1049)

# Add ChatClient Support to ChatCompletionAgent

- Resolve #10729 

## Motivation and Context

This PR enhances ChatCompletionAgent to support `IChatClient` alongside
existing IChatCompletionService, providing more flexibility in how chat
completions are handled. This enables better integration with existing
`Microsoft.Extensions.AI` types.

## Description

### Core Changes

1. Enhanced ChatCompletionAgent to:
   - Support both IChatClient and IChatCompletionService interfaces
   - Maintain backward compatibility with existing implementations

2. Updated Sample Code:
   - Added new examples in Concepts demonstrating ChatClient usage
- Updated Getting Started With Agents samples to showcase both service
types

3. Added Comprehensive Unit Tests:
   - Test coverage for Agents with ChatClient integration
   - Verification of both streaming and non-streaming scenarios

4. Added `IChatClient.AsKernelFunctionInvokingClient` extension method
to enable Kernel Function Invocation support with `IChatClient` for
solutions that target `.NET 8 LTS` only.

…ilderPattern (#12132)

- Resolves #12087 
- Add KernelChatOptions to avoid undesired leaking serializations to AI
Models.
- Added More ChatClient Extension methods to Amazon Bedrock and Azure AI
Inference
- Updated existing ChatClient using the latest changes, 
- Code improvements/clean up.

…nto feature-msextensions-ai