mv: update sparsity after moving from out-of-cone to in-cone

mv: update sparsity after moving from out-of-cone to in-cone

Originally, "git mv" a sparse file from out-of-cone to
in-cone does not update the moved file's sparsity (remove its
SKIP_WORKTREE bit). And the corresponding cache entry is, unexpectedly,
not checked out in the working tree.

Update the behavior so that:
1. Moving from out-of-cone to in-cone removes the SKIP_WORKTREE bit from
   corresponding cache entry.
2. The moved cache entry is checked out in the working tree to reflect
   the updated sparsity.

Helped-by: Victoria Dye <vdye@github.com>
Signed-off-by: Shaoxuan Yuan <shaoxuan.yuan02@gmail.com>
Acked-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>