t5318: test that '--stdin-commits' respects '--[no-]progress'

t5318: test that '--stdin-commits' respects '--[no-]progress'

The following lines were not covered in a recent line-coverage test
against Git:

  builtin/commit-graph.c
  5b6653e5 244) progress = start_delayed_progress(
  5b6653e5 268) stop_progress(&progress);

These statements are executed when both '--stdin-commits' and
'--progress' are passed. Introduce a trio of tests that exercise various
combinations of these options to ensure that these lines are covered.

More importantly, this is exercising a (somewhat) previously-ignored
feature of '--stdin-commits', which is that it respects '--progress'.
Prior to 5b6653e523 (builtin/commit-graph.c: dereference tags in
builtin, 2020-05-13), dereferencing input from '--stdin-commits' was
done inside of commit-graph.c.

Now that an additional progress meter may be generated from outside of
commit-graph.c, add a corresponding test to make sure that it also
respects '--[no]-progress'.

The other location that generates progress meter output (from d335ce8f24
(commit-graph.c: show progress of finding reachable commits,
2020-05-13)) is already covered by any test that passes '--reachable'.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>