fix(copilotcli): update elicitation handler in copilot cli to use ask tool

[DonJayamanne]

Fixes #307962

[Copilot]

Pull request overview

Updates the Copilot CLI session/MCP integration so the MCP gateway can be started with a session-associated URI (instead of an always-random URI), aligning MCP tool-call context with the originating chat session.

Changes:

• Extend ICopilotCLIMCPHandler.loadMcpConfig to accept a sessionUri and forward it to IMcpService.startMcpGateway.
• Update CopilotCLISessionService to pass a session-derived URI into MCP config loading for both session creation and session resume.
• Adjust CLI test helpers to match the updated MCP handler interface.

Show a summary per file

File	Description
extensions/copilot/src/extension/chatSessions/copilotcli/node/test/testHelpers.ts	Updates the null MCP handler stub to accept a resource/URI parameter.
extensions/copilot/src/extension/chatSessions/copilotcli/node/mcpHandler.ts	Threads a session URI through MCP config loading and into startMcpGateway.
extensions/copilot/src/extension/chatSessions/copilotcli/node/copilotcliSessionService.ts	Provides a session-derived URI to loadMcpConfig when creating/resuming CLI sessions.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1