BACKPORT: [UPSTREAM] ext2: convert to mbcache2

(Cherry-pick from commit be0726d33cb8f411945884664924bed3cb8c70ee)

The conversion is generally straightforward. We convert filesystem from
a global cache to per-fs one. Similarly to ext4 the tricky part is that
xattr block corresponding to found mbcache entry can get freed before we
get buffer lock for that block. So we have to check whether the entry is
still valid after getting the buffer lock.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Bug: 32461228