[llvm-objcopy] Route section copies through writeSectionContents
Centralize section byte copies behind a virtual helper so ELF output can later target either a memory buffer or a seekable stream. Materialize SHT_SYMTAB_SHNDX entries using the target ELF word type to preserve output endianness.
Co-authored-by: Jeremy Braun <jtbraun@meta.com>
Assisted-by: OpenAI Codex