Function create_labeled_stash 

pub fn create_labeled_stash(
    wt_repo: &mut Repository,
    branch: &str,
    worktree: &str,
) -> Result<Oid>

Create a labeled stash in wt_repo (a worktree-specific &mut Repository).

branch is the branch whose dirty state is being shelved; worktree is the host worktree name. Together they form the label used by apply_labeled_stash.