[llvm-readobj,ELF] Support --decompress/-z (#82594)

When a section has the SHF_COMPRESSED flag, -p/-x dump the compressed
content by default. In GNU readelf, if --decompress/-z is specified,
-p/-x will dump the decompressed content. This patch implements the
option.

Close #82507

(cherry picked from commit 26d71d9e)