Extract the llvm-readelf decoder to `decodeCrel` (#91280) and reuse it
for llvm-objdump.
Because the section representation of LLVMObject (`SectionRef`) is
64-bit, insufficient to hold all decoder states, `section_rel_begin` is
modified to decode CREL eagerly and hold the decoded relocations inside
ELFObjectFile<ELFT>.
The test is adapted from llvm/test/tools/llvm-readobj/ELF/crel.test.
Pull Request: https://github.com/llvm/llvm-project/pull/97382
2f37a22f10