[llvm] MachineScheduler: Improve instruction clustering (PR #137784)

[via llvm-commits]

ruiling wrote:

> Could you fix that bug first in a separate PR? Then this PR should have fewer test check changes.

See #139513. After that change, the diff here would be dropped from "176 files changed, 31670 insertions(+), 31540 deletions(-)" to "101 files changed, 25804 insertions(+), 25670 deletions(-)"

https://github.com/llvm/llvm-project/pull/137784