add -p: show user's hunk decision when selecting hunks

add -p: show user's hunk decision when selecting hunks

When a user is interactively deciding which hunks to use or skip for
staging, unstaging, stashing etc, there is no way to know the
decision previously chosen for a hunk when navigating through the
previous and next hunks using K/J respectively.

Improve the UI to explicitly show if a user has previously decided to
use a hunk (by pressing 'y') or skip the hunk (by pressing 'n').
This will improve clarity when and aid the navigation process for the
user.

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