ELF: Store EhInputSection relocations to simplify code. NFC
Store relocations directly as `SmallVector<Relocation, 0>` within
EhInputSection to avoid processing different relocation formats
(REL/RELA/CREL) throughout the codebase.
Next: Refactor RelocationScanner to utilize EhInputSection::rels
Pull Request: https://github.com/llvm/llvm-project/pull/161041