[llvm] [MISched] Add statistics for heuristics (PR #137981)

[Min-Yih Hsu via llvm-commits]

https://github.com/mshockwave commented:

On a related note, I've been thinking about improving the trace output of MachineScheduler because I alway found some messages a bit difficult to comprehend, I'm wondering what's your thoughts?

https://github.com/llvm/llvm-project/pull/137981