Partition SuperPMI replay task (#66065)

Partition SuperPMI replay task (#66065)

* Partition SuperPMI replay task

Split per-platform/architecture work into multiple partitions to increase pipeline
parallelism and reduce overall job time. The partitions are sets of
different JitStressRegs options.

We could create a partition for each JitStressRegs option, but the concern
is that there is potentially a lot of overhead downloading the large set
of MCH files, and we might want to share that overhead between work partitions.

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