ext4: Track metadata bhs in fs-private inode part

ext4: Track metadata bhs in fs-private inode part

Track metadata bhs for an inode in fs-private part of the inode. We need
the tracking only for nojournal mode so this is somewhat wasteful. We
can relatively easily make the mapping_metadata_bhs struct dynamically
allocated similarly to how we treat jbd2_inode but let's leave that for
ext4 specific series once the dust settles a bit.

Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260326095354.16340-82-jack@suse.cz
Signed-off-by: Christian Brauner <brauner@kernel.org>