[llvm] yaml2obj: Implement Coverage mapping format (PR #129472)

[James Henderson via llvm-commits]

jh7370 wrote:

If this is ready for a round of review, please let me know. Please note that I have scheduled time off between the 14th and 28th of this month, so won't be able to review during this time. @MaskRay may be a good alternative reviewer of the yaml2obj stuff, if he's available.

https://github.com/llvm/llvm-project/pull/129472