Add event emitters for workspace folder and worktree changes

[DonJayamanne]

Introduce event emitters to notify changes in workspace folders and worktrees, enhancing cache management for affected sessions. This update improves responsiveness to changes in the workspace environment.

For #309466

[Copilot]

Pull request overview

This PR adds change-notification plumbing around session diff/changes caching so the Copilot chat sessions UI can respond when workspace folders/worktrees change and when git state changes invalidate cached diffs.

Changes:

• Introduces per-session events for invalidation of workspace-folder/worktree change caches.
• Refactors repository-state handling into clearChangesCacheForAffectedSessions(...) and calls it on repo state changes and request completion.
• Adds an additional in-provider cachedChanges layer to avoid “diff info flashing” during refresh/resolve cycles.

Show a summary per file

File	Description
extensions/copilot/src/extension/chatSessions/vscode-node/sessionRequestLifecycle.ts	Clears changes cache for other sessions in the same folder after request completion.
extensions/copilot/src/extension/chatSessions/vscode-node/copilotCLIChatSessionsContribution.ts	Adds local cachedChanges layer and invokes cache clearing after request completion.
extensions/copilot/src/extension/chatSessions/vscode-node/copilotCLIChatSessions.ts	Adds local cachedChanges layer and wires new invalidation events to refresh items in controller path.
extensions/copilot/src/extension/chatSessions/vscode-node/chatSessions.ts	Stops passing an item provider into ChatSessionRepositoryTracker in controller path.
extensions/copilot/src/extension/chatSessions/vscode-node/chatSessionWorktreeServiceImpl.ts	Emits a new event when worktree changes cache is cleared.
extensions/copilot/src/extension/chatSessions/vscode-node/chatSessionWorkspaceFolderServiceImpl.ts	Emits a new event when workspace-folder changes cache is invalidated.
extensions/copilot/src/extension/chatSessions/vscode-node/chatSessionRepositoryTracker.ts	Extracts shared invalidation/refresh logic into clearChangesCacheForAffectedSessions(...).
extensions/copilot/src/extension/chatSessions/common/chatSessionWorktreeService.ts	Adds onDidChangeWorktreeChanges to the service interface.
extensions/copilot/src/extension/chatSessions/common/chatSessionWorkspaceFolderService.ts	Adds onDidChangeWorkspaceFolderChanges to the service interface.

Copilot's findings

Comments suppressed due to low confidence (1)

extensions/copilot/src/extension/chatSessions/vscode-node/copilotCLIChatSessions.ts:216

• The new cachedChanges layer can return stale diffs after an invalidation. refreshSession() calls toChatSessionItem() without includeChanges, and toChatSessionItem() will keep using this.cachedChanges.get(session.id) even when hasCachedChanges() is false (i.e. the underlying caches were cleared). When handling onDidChangeWorkspaceFolderChanges/onDidChangeWorktreeChanges, consider clearing cachedChanges for that sessionId (or adjusting toChatSessionItem to ignore cachedChanges when underlying caches were invalidated).

		this._register(this._workspaceFolderService.onDidChangeWorkspaceFolderChanges(e => {
			this.refreshSession({ reason: 'update', sessionId: e.sessionId });
		}));
		this._register(chatSessionWorktreeService.onDidChangeWorktreeChanges(e => {
			this.refreshSession({ reason: 'update', sessionId: e.sessionId });
		}));

• Files reviewed: 9/9 changed files
• Comments generated: 5