add-patch: allow all-or-none application of patches

add-patch: allow all-or-none application of patches

When the flag `--no-auto-advance` is used with `--patch`,
if the user has decided `USE` on a hunk in a file, goes to another
file, and then returns to this file and changes the previous
decision on the hunk to `SKIP`, because the patch has already
been applied, the last decision is not registered and the now
SKIPPED hunk is still applied.

Move the logic for applying patches into a function so that we can
reuse this logic to implement the all or non application of the patches
after the user is done with the hunk selection.

Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>