refactor(copilotcli): enhance session handling with branch name generation

[DonJayamanne]

No description provided.

[Copilot]

Pull request overview

Refactors the Copilot CLI chat session flow to optionally generate an AI-suggested git branch name for new sessions and plumb it into folder/worktree initialization, gated by configuration.

Changes:

• Adds an optional GitBranchNameGenerator dependency to the Copilot CLI session participant (V1) and forwards a newBranch promise into folder/worktree initialization.
• Wires up the branch name generator in the Copilot CLI services registration (V1) when chat.cli.aiGenerateBranchNames.enabled is enabled.
• Updates unit tests to account for the new constructor parameter.

Show a summary per file

File	Description
extensions/copilot/src/extension/chatSessions/vscode-node/copilotCLIChatSessionsContribution.ts	Generates/forwards an AI branch name during session creation and passes it into folder repository initialization.
extensions/copilot/src/extension/chatSessions/vscode-node/chatSessions.ts	Conditionally instantiates and injects GitBranchNameGenerator into the V1 participant based on configuration.
extensions/copilot/src/extension/chatSessions/vscode-node/test/copilotCLIChatSessionParticipant.spec.ts	Updates test instantiations/import ordering for the participant’s new constructor signature.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 2