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

These are picked up from getMemOperandsWithOffsetWidth but weren't then
being passed through to shouldClusterMemOps, which forces backends to
collect the information again if they want to use the kind of heuristics
typically used for the similar shouldScheduleLoadsNear function (e.g.
checking the offset is within 1 cache line).

This patch just adds the parameters, but doesn't attempt to use them.
There is potential to use them in the current PPC and AArch64
shouldClusterMemOps implementation, and I intend to use the offset in
the heuristic for RISC-V. I've left these for future patches in the
interest of being as incremental as possible.

As noted in the review and in an inline FIXME, an ElementCount-style abstraction may later be used to condense these two parameters to one argument. ElementCount isn't quite suitable as it doesn't support negative offsets.