t1092: mv directory from out-of-cone to in-cone

t1092: mv directory from out-of-cone to in-cone

Add test for "mv: add check_dir_in_index() and solve general dir check
issue" in this series.

This change tests the following:

1. mv <source> as a directory on the sparse index boundary (where it
   would be a sparse directory in a sparse index).
2. mv <source> as a directory which is deeper than the boundary (so
   the sparse index would expand in the cache_name_pos() method).

These tests can be written now for correctness, but later the first case
can be updated to use the 'ensure_not_expanded' helper in t1092.

Suggested-by: Derrick Stolee <redacted>
Signed-off-by: Shaoxuan Yuan <redacted>
Acked-by: Derrick Stolee <redacted>
Signed-off-by: Junio C Hamano <redacted>