fsck.erofs: support --extract=X like fsck.cramfs to extract to path X

[Gao Xiang]

Hi Igor,

On Fri, Dec 10, 2021 at 02:48:30AM +0200, Igor Eisberg wrote:
> * Extracts dirs, regular files and symlinks (overwrite enabled with a
> erofs_warn, mainly for use with WSL, in case certain files in img exist in
> different letter cases under the same dir, i.e. "path/to/file/alarm" and
> "path/to/file/Alarm").
> * Raw and compressed data chunks are handled with a unified function to
> avoid repeats, compressed data is verified lineary
> (with EROFS_GET_BLOCKS_FIEMAP) instead of lookback, as it's problematic to
> extract data when looping backwards.
> * Also refactored some function names and strings for consistency.
> 
> Please let me know if anything has to be changed.
> 
> Best regards to Mr. Xiang!

Thanks for your effort and patch! I might need to seek a whole free
slot to look at this (maybe this weekend...). Before that, would you
mind sending a patch with your "Signed-off-by:" [1] and using
"git format-patch" to format a patch?

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst#n382

Thanks,
Gao Xiang