llvm-cov: Rename MappingRegion to coverage::CountedRegion (NFC)

This name was too similar to CoverageMappingRegion, and the type
really belongs in the coverage library anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217416 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed