Add oneAPI back-end.
Created by: maleadt
TODO:
-
Don't use Float64 in tests; the oneAPI CI GPU doesn't support it -
Events: do we need to signal the event when creating it? Other back-ends do it, but that seems fishy. -
wait: do we need to support an invocation with no queue argument (having it default to the global queue)? again, other back-ends support this, but it just seems wrong to use the global queue (which is generally not used by KA.jl) for signalling an event.