Make alpaka work with SYCL

[StewMH]

I added a queue argument for vecmem::sycl::copy. Not in a very clean way, but this all needs cleaned up (as discussed with @CrossR) and hopefully coming soon in an MR from him or me.

With this I can get the alpaka seeding example to work on the CERN GPU Flex 170:

==> Statistics ...
- read    77602 spacepoints
- created  (cpu)  0 seeds
- created (alpaka)  66540 seeds
==>Elapsed times...
            Hit reading  (cpu)  1012 ms
              Seeding (alpaka)  6472 ms
         Track params (alpaka)  1847 ms
                     Wall time  9334 ms

It's very slow compared to the CUDA implementation, but I think this is largely because I had to enable FP64 emulation:

• Some Intel GPUs do not support the double type for device code. alpaka will not check this.
  You can enable software emulation for double precision types with

export IGC_EnableDPEmulation=1
export OverrideDefaultFP64Settings=1

[krasznaa]

Overall, very happy about the developments. But we'll indeed need to find some good way of passing in the common ::sycl::queue from the outside to all the SYCL objects.

I also wonder where we could pass a queue to Alpaka. Or how we could get the queue that Alpaka uses. Since all of these will have to be synced up. 🤔

[krasznaa]

Not for this PR, but we should try to find a way of using "factory functions" for instantiating the appropriate type of memory resource and copy objects. To eliminate all appearances of preprocessor statements from the "user code".

But for this PR, as long as you clean up the CMake code a little using a new macro, I'll be happy to let it through. (The change in the main CMakeLists.txt file affects others as well, that's why I'd like to get that fixed.)

[sonarqubecloud]

Please retry analysis of this Pull-Request directly on SonarQube Cloud

[krasznaa]

Okay, this setup I can live with. 😄

[StewMH]

Think this is good to go now

[krasznaa]

Sorry, didn't realize that you would not be allowed to merge once I approved it. 😛