Merge branch 'es/worktree-duplicate-paths'

Merge branch 'es/worktree-duplicate-paths'

The same worktree directory must be registered only once, but
"git worktree move" allowed this invariant to be violated, which
has been corrected.

* es/worktree-duplicate-paths:
  worktree: make "move" refuse to move atop missing registered worktree
  worktree: generalize candidate worktree path validation
  worktree: prune linked worktree referencing main worktree path
  worktree: prune duplicate entries referencing same worktree path
  worktree: make high-level pruning re-usable
  worktree: give "should be pruned?" function more meaningful name
  worktree: factor out repeated string literal