t: convert grep assertions to test_grep

t: convert grep assertions to test_grep

Replace bare grep with test_grep in test assertions across the
suite, including sourced test helpers (lib-*.sh, *-tests.sh).
test_grep prints the contents of the file being searched on
failure, making debugging easier than a bare grep which fails
silently.

Only assertion-style greps are converted: grep used as a filter
in pipelines, command substitutions, conditionals, or with
redirected I/O is left as-is with a "# lint-ok" annotation.
Existing '! test_grep' calls are rewritten to 'test_grep !' so
that the diagnostic output is preserved on failure.

test_grep requires the file it reads to exist, so '! grep'
assertions that inspect a file whose presence is conditional need
care.  In t5537 the '.git/shallow' file is still present after the
repack (the client remains shallow), so the assertion is
converted like any other.  In t1400 the '.git/packed-refs' file
exists only with the files backend, so its check is guarded with a
REFFILES prerequisite; the backend-agnostic 'git show-ref' check
that follows still runs under every backend.  In t7450 'git~2' is
the NTFS 8.3 short name of a '..git' file and only exists
when 8.3 short-name generation is enabled, so its check is guarded
with a 'test -f' on the path and uses test_grep inside the guard,
the same shape as t1400 (a plain test_grep would BUG when the
short name is absent).

The conversion was generated using a grep-assertion linter
(greplint.pl, added in the following commit) to identify bare
grep calls at command position.  To reproduce, from the t/
directory:

    # Step 1: annotate the two data-filter greps (grep produces
    # data, not a verdict) so the linter skips them.
    sed -i '/grep -vf before commits\.raw/s/$/ # lint-ok: data filter/' \
        t5326-multi-pack-bitmaps.sh
    sed -i '/grep -E "^\[0-9a-f\].*|| :/s/$/ # lint-ok: data filter/' \
        t5702-protocol-v2.sh

    # Step 1b: two '! grep' assertions need more than a mechanical
    # conversion; handle them by hand before the linter-driven steps
    # below so it leaves them alone.
    #
    # t1400: '.git/packed-refs' is absent under reftable, so guard the
    # check with REFFILES (a plain test_grep would BUG on the missing
    # file):
    #
    #      git update-ref -d HEAD $B &&
    #  -   ! grep "$m" .git/packed-refs &&
    #  +   if test_have_prereq REFFILES
    #  +   then
    #  +           test_grep ! "$m" .git/packed-refs
    #  +   fi &&
    #      test_must_fail git show-ref --verify -q $m
    #
    # t7450: git~2 is an NTFS 8.3 short name that exists only when
    # short-name generation is enabled, so guard the check on its
    # presence with 'test -f' and note in a comment why the path can
    # be absent (a plain test_grep would BUG when it is):
    #
    #  -   ! grep gitdir squatting-clone/d/a/git~2
    #  +   if test -f squatting-clone/d/a/git~2
    #  +   then
    #  +           test_grep ! gitdir squatting-clone/d/a/git~2
    #  +   fi

    # Step 2: reorder pre-existing '! test_grep' to 'test_grep !'
    # (must come before steps 3-4 so greplint does not see them)
    sed -i 's/! test_grep/test_grep !/' t0031-lockfile-pid.sh
    sed -i 's/! test_grep/test_grep !/' t5300-pack-object.sh
    sed -i 's/! test_grep/test_grep !/' t5319-multi-pack-index.sh

    # Step 3: convert '! grep' -> 'test_grep !'
    perl greplint.pl *.sh 2>&1 | cut -d: -f1,2 |
    while IFS=: read f l; do
        sed -i "${l}s/! *grep/test_grep !/" "$f"
    done

    # Step 4: convert remaining 'grep' -> 'test_grep'
    perl greplint.pl *.sh 2>&1 | cut -d: -f1,2 |
    while IFS=: read f l; do
        sed -i "${l}s/grep/test_grep/" "$f"
    done

To verify, run: make -C t test-greplint

Signed-off-by: Michael Montalbo <redacted>
Signed-off-by: Junio C Hamano <redacted>