[llvm] [MachineScheduler][NFCI] Add Offset and OffsetIsScalable args to shouldClusterMemOps (PR #73778)

[Alex Bradbury via llvm-commits]

asb wrote:

Apologies for the messy extra pushes. I missed a doc comment in the first version of the patch, and then had to back out a claim that Offset2 is always greater than Offset1 (this isn't actually guaranteed from what I can see). Hopefully all resolved and ready for review now.

https://github.com/llvm/llvm-project/pull/73778