erofs: error out obviously illegal extents in advance

Detect some corrupted extent cases during metadata parsing rather
than letting them result in harmless decompression failures later:

 - For full-reference compressed extents, the compressed size must
   not exceed the decompressed size, which is a strict on-disk
   layout constraint;

 - For plain (shifted/interlaced) extents, the decoded size must
   not exceed the encoded size, even accounting for partial decoding.

Both ways work but it should be better to report illegal extents as
metadata layout violations rather than deferring as decompression
failure.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>