hfs: rework hfsplus_readdir() logic

hfs: rework hfsplus_readdir() logic

The xfstests' test-case generic/637 fails with error:

FSTYP -- hfs
PLATFORM -- Linux/x86_64 kvm-xfstests 6.15.0-rc4-xfstests-g00b827f0cffa #1 SMP PREEMPT_DYNAMIC Fri May 25
MKFS_OPTIONS -- /dev/vdc
MOUNT_OPTIONS -- /dev/vdc /vdc

QA output created by 637
entries 7 and 8 have duplicate d_off 8
Found unlinked files in open dir (see xfstests-dev/results//generic/637.full for details)

Likewise HFS+, currently, HFS has very complicated and
fragile logic of rd->file->f_pos correction in hfs_delete_cat().
This patch removes this logic and it stores the current
pos into hfs_readdir_data. Finally, if rd->pos == ctx->pos
then hfs_readdir() tries to find the position in
b-tree's node by means of hfs_cat_key. This position is
used to re-start the folder's content traversal.

sudo ./check generic/637
FSTYP         -- hfs
PLATFORM      -- Linux/x86_64 hfsplus-testing-0001 7.1.0-rc1+ #55 SMP PREEMPT_DYNAMIC Tue May 19 15:18:02 PDT 2026
MKFS_OPTIONS  -- /dev/loop51
MOUNT_OPTIONS -- /dev/loop51 /mnt/scratch

generic/637  32s ...  31s
Ran: generic/637
Passed all 1 tests

Closes: https://github.com/hfs-linux-kernel/hfs-linux-kernel/issues/65
cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
cc: Yangtao Li <frank.li@vivo.com>
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/r/20260519222811.1311071-2-slava@dubeyko.com
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>