Merge branch 'ds/worktree-docs'

Tighten the language around "working tree" and "worktree" in the
docs.

* ds/worktree-docs:
  worktree: use 'worktree' over 'working tree'
  worktree: use 'worktree' over 'working tree'
  worktree: use 'worktree' over 'working tree'
  worktree: use 'worktree' over 'working tree'
  worktree: use 'worktree' over 'working tree'
  worktree: use 'worktree' over 'working tree'
  worktree: use 'worktree' over 'working tree'
  worktree: extract checkout_worktree()
  worktree: extract copy_sparse_checkout()
  worktree: extract copy_filtered_worktree_config()
  worktree: combine two translatable messages

Author: gitster