The command line completion (in contrib/) learned to complete
subcommands and arguments to "git worktree".
* sg/completion-worktree:
completion: list paths and refs for 'git worktree add'
completion: list existing working trees for 'git worktree' subcommands
completion: simplify completing 'git worktree' subcommands and options
completion: return the index of found word from __git_find_on_cmdline()
completion: clean up the __git_find_on_cmdline() helper function
t9902-completion: add tests for the __git_find_on_cmdline() helper
fec1ff97c2