Sessions - add noTrack option to worktree creation and adopt new option

[lszomoru]

Fixes #308465

[Copilot]

Pull request overview

This PR extends the Git extension’s worktree creation plumbing to support a noTrack option (mapped to git worktree add --no-track) and adopts that option in Copilot Sessions worktree creation to avoid configuring upstream tracking for the created branch.

Changes:

• Add an optional noTrack?: boolean to Repository.createWorktree(...) and wire it through to the underlying git worktree add invocation.
• Update the Git extension API typings and API wrapper to expose the new option.
• Update Copilot’s git service abstractions/mocks and set noTrack: true when creating session worktrees.

Show a summary per file

File	Description
extensions/git/src/repository.ts	Thread noTrack through Repository.createWorktree into the underlying git repository implementation.
extensions/git/src/git.ts	Add support for --no-track in worktree add argument construction.
extensions/git/src/api/git.d.ts	Expose the new noTrack option on the Git extension’s public createWorktree API typing.
extensions/git/src/api/api1.ts	Keep the API wrapper signature in sync with the updated createWorktree options.
extensions/copilot/src/platform/test/node/simulationWorkspaceServices.ts	Update test service interface typing to include noTrack.
extensions/copilot/src/platform/ignore/node/test/mockGitService.ts	Update mock git service typing to include noTrack.
extensions/copilot/src/platform/git/vscode/git.d.ts	Update Copilot’s vendored Git API typing to include noTrack.
extensions/copilot/src/platform/git/vscode-node/gitServiceImpl.ts	Update createWorktree signature to accept and forward noTrack.
extensions/copilot/src/platform/git/common/gitService.ts	Update IGitService.createWorktree options typing to include noTrack.
extensions/copilot/src/extension/chatSessions/vscode-node/chatSessionWorktreeServiceImpl.ts	Adopt noTrack: true for Copilot session worktree creation.

Copilot's findings

• Files reviewed: 8/10 changed files
• Comments generated: 0