erofs: add on-disk compressed tail-packing inline support

Introduces erofs compressed tail-packing inline support.

This approach adds a new field called `h_idata_size' in the
per-file compression header to indicate the encoded size of
each tail-packing pcluster.

At runtime, it will find the start logical offset of the tail
pcluster when initializing per-inode zmap and record such
extent (headlcn, idataoff) information to the in-memory inode.
Therefore, follow-on requests can directly recognize if one
pcluster is a tail-packing inline pcluster or not.

Link: https://lore.kernel.org/r/20211228054604.114518-6-hsiangkao@linux.alibaba.com


Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Yue Hu <huyue2@yulong.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>