[llvm] [MISched] Extend overridePostRASchedPolicy to support per-function scheduling direction (PR #149297)

[Jon Roelofs via llvm-commits]

jroelofs wrote:

> Plus, fundamentally this API is called per region rather than per function

I was thinking the same thing. Alternatively, you could pass the `MachineBasicBlock`, since that's what we have available in `initPolicy`.

https://github.com/llvm/llvm-project/pull/149297