.Net: Contextual function provider

[SergeyMenshykh]

Motivation, Context, and Description

This PR adds functionality that allows AI agents to advertise functions relevant to the current context, rather than advertising all available functions.

The functionality is implemented by two components:

• The FunctionStore class is responsible for the vectorization of functions, upserting them into the provided vector store, and performing vector searches. This class is internal at the moment as it's used only by the ContextualFunctionProvider class. Later, it might be promoted to public if required.
• The ContextualFunctionProvider class delegates function vectorization and persistence to the FunctionStore. It vectorizes the current context and delegates the vector search to the FunctionStore class again.

Logging will be added in follow-up PRs.

Contributes to: #10074

[Copilot]

Pull Request Overview

Adds a contextual function selection capability by vectorizing available functions and retrieving only those relevant to the current chat context.

• Introduces FunctionStore and its options to index and search functions via a vector store
• Adds ContextualFunctionProvider and corresponding options to plug into chat-based agents
• Updates sample project to demonstrate usage and adds a new ModelContextProtocol dependency

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
dotnet/src/SemanticKernel.Core/Functions/ContextualSelection/FunctionStoreOptions.cs	Defines options for function vectorization and retrieval
dotnet/src/SemanticKernel.Core/Functions/ContextualSelection/FunctionStore.cs	Implements vector store indexing and search logic
dotnet/src/SemanticKernel.Core/Functions/ContextualSelection/ContextualFunctionProviderOptions.cs	Defines public options for the contextual provider
dotnet/src/SemanticKernel.Core/Functions/ContextualSelection/ContextualFunctionProvider.cs	Wraps FunctionStore to provide an AI context with relevant functions
dotnet/samples/Concepts/Concepts.csproj	Adds ModelContextProtocol package reference
dotnet/samples/Concepts/Agents/ChatCompletion_ContextualFunctionSelection.cs	Sample showing how to wire up the contextual provider

Comments suppressed due to low confidence (1)

dotnet/samples/Concepts/Agents/ChatCompletion_ContextualFunctionSelection.cs:38

• [nitpick] The agent name uses GithubAssistant; update it to GitHubAssistant to match correct casing of the GitHub brand.

Name = "GithubAssistant",