[lld] [lld][ELF] Implement merged .debug_names section. (PR #86508)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> (Reading. I find `ELFT::TargetEndianness` too long. Proposed #86604 to allow `ELFT::Endian`. No action needed yet)

We ended up with `ELFT::Endianness`. The next update can switch to  `ELFT::Endianness`

https://github.com/llvm/llvm-project/pull/86508