badblocks: improve badblocks_clear() for multiple ranges handling

With the fundamental ideas and helper routines from badblocks_set()
improvement, clearing bad block for multiple ranges is much simpler.

With a similar idea from badblocks_set() improvement, this patch
simplifies bad block range clearing into 5 situations. No matter how
complicated the clearing condition is, we just look at the head part
of clearing range with relative already set bad block range from the
bad block table. The rested part will be handled in next run of the
while-loop.

Based on existing helpers added from badblocks_set(), this patch adds
two more helpers,
- front_clear()
  Clear the bad block range from bad block table which is front
  overlapped with the clearing range.
- front_splitting_clear()
  Handle the condition that the clearing range hits middle of an
  already set bad block range from bad block table.

Similar as badblocks_set(), the first part of clearing range is handled
with relative bad block range which is find by prev_badblocks(). In most
cases a valid hint is provided to prev_badblocks() to avoid unnecessary
bad block table iteration.

This patch also explains the detail algorithm code comments at beginning
of badblocks.c, including which five simplified situations are
categrized and how all the bad block range clearing conditions are
handled by these five situations.

Again, in order to make the code review easier and avoid the code
changes mixed together, this patch does not modify badblock_clear() and
implement another routine called _badblock_clear() for the improvement.
Later patch will delete current code of badblock_clear() and make it as
a wrapper to _badblock_clear(), so the code change can be much clear for
review.
Signed-off-by: Coly Li <colyli@suse.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Geliang Tang <geliang.tang@suse.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: NeilBrown <neilb@suse.de>
Cc: Vishal L Verma <vishal.l.verma@intel.com>
Cc: Xiao Ni <xni@redhat.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Acked-by: Geliang Tang <geliang.tang@suse.com>
Link: https://lore.kernel.org/r/20230811170513.2300-5-colyli@suse.deSigned-off-by: Jens Axboe <axboe@kernel.dk>