sparse-index.h: move declarations for sparse-index.c from cache.h
Note in particular that this reverses the decision made in 118a2e8bde0
("cache: move ensure_full_index() to cache.h", 2021-04-01).
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
authored by