[llvm] [ELFYAML] Introduce the external interface `CustomSection` (PR #115707)

[Jessica Paquette via llvm-commits]

ornata wrote:

> I have a plan to integrate covmap encoder with LLVMCoverage and YAML sections. I am proposing "plugin" since I want to avoid for LLVMObjectYAML depending on LLVMCoverage. LLVMObjectYAML may be unaware of blob contents defined externally.

What would the disadvantage of depending on LLVMCoverage be?

https://github.com/llvm/llvm-project/pull/115707