bundle: show progress on "unbundle"

bundle: show progress on "unbundle"

The "unbundle" command added in 2e0afafebd8 (Add git-bundle: move
objects and references by archive, 2007-02-22) did not show progress
output, even though the underlying API learned how to show progress in
be042aff24c (Teach progress eye-candy to fetch_refs_from_bundle(),
2011-09-18).

Now we'll show "Unbundling objects" using the new --progress-title
option to "git index-pack", to go with its existing "Receiving
objects" and "Indexing objects" (which it shows when invoked with
"--stdin", and with a pack file, respectively).

Unlike "git bundle create" we don't handle "--quiet" here, nor
"--all-progress" and "--all-progress-implied". Those are all specific
to "create" (and "verify", in the case of "--quiet").

The structure of the existing documentation is a bit unclear, e.g. the
documentation for the "--quiet" option added in
79862b6b77c (bundle-create: progress output control, 2019-11-10) only
describes how it works for "create", and not for "verify". That and
other issues in it should be fixed, but I'd like to avoid untangling
that mess right now. Let's just support the standard "--no-progress"
implicitly here, and leave cleaning up the general behavior of "git
bundle" for a later change.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>