std::is_trivially_copyable constraint on kernel type

[jasminmohnke]

While #2198 clears the issue we had with the check on kernel arguments being trivially copyable as discussed in #2195, unfortunately I am running into a comparable issue with the check done on the kernel itself in

alpaka/include/alpaka/kernel/Traits.hpp

Lines 269 to 271 in a4142d3

	std::is_trivially_copyable_v<TKernelFnObj> || __nv_is_extended_device_lambda_closure_type(TKernelFnObj)
	|| __nv_is_extended_host_device_lambda_closure_type(TKernelFnObj),
	"Kernels must be trivially copyable or an extended CUDA lambda expression!");

If, for instance, a user kernel has a member that is of a type such as described previously (#2195), std::is_trivially_copyable evaluates to false as well. A trait similarly to the one you introduced for the kernel argument would be helpful to have for the kernel as well.

[psychocoderHPC]

Thanks for opening the issue, we will have a look into it.