[llvm] [llvm-cov] format cells in code coverage report with 0/0 branches/functions/lines differently (PR #75780)

[NAKAMURA Takumi via llvm-commits]

https://github.com/chapuni approved this pull request.

Thanks. This is a good improvement for the UX!
I pre-approve with one nit.

I would like to wait for at least one more for the approval. @petrhosek , how is this?

https://github.com/llvm/llvm-project/pull/75780