[SYCL] Implement reduction properties extension (#15804)
Adds support for initialize_to_identity and deterministic properties.
Since this extension is only experimental, the implementation here
avoids making significant changes to reduction-related classes (e.g,
reducer).
A more straightforward implementation that attaches a compile-time
property list to these classes is possible, but may be considered an ABI
break.
---
A note to reviewers: it occurred to me that
`IsDeterministicOperator<BinaryOperation>` might actually be better as
`IsDeterministicOperator<T, BinaryOperation>`, so that the
implementation can infer that it's safe to use the faster reductions for
certain types (e.g., `int` and `sycl::plus<>()` can safely use atomics)
but I wanted to get your feedback on the proposed approach before going
any further.
**EDIT**: To clarify, I think such changes to `IsDeterministicOperator`
could be left until a future PR, since the behavior of the
`deterministic` property as implemented here should match the legacy
`SYCL_DETERMINISTIC_REDUCTION` macro. We could implement optimizations
later.
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Signed-off-by: John Pennycook <john.pennycook@intel.com>
