Merge branch 'sy/mv-out-of-cone'

"git mv A B" in a sparsely populated working tree can be asked to
move a path between directories that are "in cone" (i.e. expected
to be materialized in the working tree) and "out of cone"
(i.e. expected to be hidden).  The handling of such cases has been
improved.

* sy/mv-out-of-cone:
  mv: add check_dir_in_index() and solve general dir check issue
  mv: use flags mode for update_mode
  mv: check if <destination> exists in index to handle overwriting
  mv: check if out-of-cone file exists in index with SKIP_WORKTREE bit
  mv: decouple if/else-if checks using goto
  mv: update sparsity after moving from out-of-cone to in-cone
  t1092: mv directory from out-of-cone to in-cone
  t7002: add tests for moving out-of-cone file/directory