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

[Alexander Yermolovich via llvm-commits]

ayermolo wrote:

What does everyone thinks about refactoring the debug names code out of SythenticSections.cpp to DebugNamesSyntheticSection.cpp or something like that? (followup commit is fine)
That file is almost 5k lines of code and is getting unwieldy.

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