erofs: tidy up EROFS on-disk naming
- Get rid of all "vle" (variable-length extents) expressions
since they only expand overall name lengths unnecessarily;
- Rename COMPRESSION_LEGACY to COMPRESSED_FULL;
- Move on-disk directory definitions ahead of compression;
- Drop unused extended attribute definitions;
- Move inode ondisk union `i_u` out as `union erofs_inode_i_u`.
No actual logical change.
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230331063149.25611-1-hsiangkao@linux.alibaba.com