[WIP] Adding multi-device support through the IREE compilation pipelines.

[benvanik]

(incremental PRs coming soon, this is mostly for ease of rebasing test failures as the bots find them)

[sogartar]

@benvanik, great work! I was doing a sneak preview and I am wondering if the intended way of setting an affinity of an arbitrary operation is through the stream.affinity attribute? E.g.

stream.affinity = #hal.device.affinity<@device>

Or there is an op interface for that, which hides this detail?

Another forward looking question that I have is how would dynamic number of device/queues be handled? If we bake things into an attribute we can't handle that.

[benvanik]

Closing now in favor of a shared/multi-device to main merge PR.