builtin-commit: refactor short-status code into wt-status.c

builtin-commit: refactor short-status code into wt-status.c

Currently, builtin-commit.c contains most code producing the
short-status output, whereas wt-status.c contains most of the code for
the long format.

Refactor so that most of the long and short format producing code
resides in wt-status.c and is named analogously.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>