.Net: Allow chat history mutation from auto-function invocation filters

[SergeyMenshykh]

Motivation and Context

Today, {Azure} OpenAI connectors don't allow auto-function invocation filters to update/mutate chat history. The mutation can be useful to reduce the number of tokens sent to LLM by removing no longer needed function-calling messages from the chat history.

Partially closes: #7590. The MistralAI connector will be updated in a separate PR.

Description

This PR updates the ClientCore class to generate a list of messages to send to the LLM based on the latest chat history for every function-calling loop iteration, rather than separately updating the list of LLM messages and chat history.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[RogerBarreto]

@SergeyMenshykh in the description says a change in the behavior but I'm just seeing UnitTests added as part of the PR, is that correct?