FROMGIT: f2fs: Introduce linear search for dentries

This patch addresses an issue where some files in case-insensitive
directories become inaccessible due to changes in how the kernel function,
utf8_casefold(), generates case-folded strings from the commit 5c26d2f1
("unicode: Don't special case ignorable code points").

F2FS uses these case-folded names to calculate hash values for locating
dentries and stores them on disk. Since utf8_casefold() can produce
different output across kernel versions, stored hash values and newly
calculated hash values may differ. This results in affected files no
longer being found via the hash-based lookup.

To resolve this, the patch introduces a linear search fallback.
If the initial hash-based search fails, F2FS will sequentially scan the
directory entries.

Fixes: 5c26d2f1 ("unicode: Don't special case ignorable code points")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=219586


Change-Id: Ib37b714040d6b969b3161c50e3c02205af7c688c
Signed-off-by: Daniel Lee <chullee@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
(cherry picked from commit 91b587ba https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git

 dev)
Bug: 384758596
Bug: 392735861
Signed-off-by: Daniel Rosenberg <drosen@google.com>
(cherry picked from commit dea08dbb)