[flang] [llvm] [flang][OpenMP] Track reachable metadirective replacements (PR #219014)

[via llvm-commits]

MattPD wrote:

Could the PR description also cover the shared OpenMP scoring changes and their effects on DECLARE VARIANT and metadirective lowering? The current description presents ranking as unchanged, but those changes will be part of the squash commit.

https://github.com/llvm/llvm-project/pull/219014