ext4: refactor choose group to scan group

ext4: refactor choose group to scan group

This commit converts the `choose group` logic to `scan group` using
previously prepared helper functions. This allows us to leverage xarrays
for ordered non-linear traversal, thereby mitigating the "bouncing" issue
inherent in the `choose group` mechanism.

This also decouples linear and non-linear traversals, leading to cleaner
and more readable code.

Key changes:

 * ext4_mb_choose_next_group() is refactored to ext4_mb_scan_groups().

 * Replaced ext4_mb_good_group() with ext4_mb_scan_group() in non-linear
   traversals, and related functions now return error codes instead of
   group info.

 * Added ext4_mb_scan_groups_linear() for performing linear scans starting
   from a specific group for a set number of times.

 * Linear scans now execute up to sbi->s_mb_max_linear_groups times,
   so ac_groups_linear_remaining is removed as it's no longer used.

 * ac->ac_criteria is now used directly instead of passing cr around.
   Also, ac->ac_criteria is incremented directly after groups scan fails
   for the corresponding criteria.

 * Since we're now directly scanning groups instead of finding a good group
   then scanning, the following variables and flags are no longer needed,
   s_bal_cX_groups_considered is sufficient.

    s_bal_p2_aligned_bad_suggestions
    s_bal_goal_fast_bad_suggestions
    s_bal_best_avail_bad_suggestions
    EXT4_MB_CR_POWER2_ALIGNED_OPTIMIZED
    EXT4_MB_CR_GOAL_LEN_FAST_OPTIMIZED
    EXT4_MB_CR_BEST_AVAIL_LEN_OPTIMIZED

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250714130327.1830534-17-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>