PortableTestObjects

Define the portable SoA-based data formats

Notes:

• define a full dictionary for portabletest::TestSoA and portabletest::TestHostCollection
• do not define a dictionary for alpaka_serial_sync::portabletest::TestDeviceCollection, because it is the same class as portabletest::TestHostCollection;
• define the dictionary for alpaka_cuda_async::portabletest::TestDeviceCollection as transient only;
• the dictionary for alpaka_cuda_async::portabletest::TestDeviceCollection should be defined in a separate library, to factor out the CUDA dependency.