Implement sycl_khr_work_item_queries extension

[0x12CC]

Implements the extension defined in KhronosGroup/SYCL-Docs#682.

[steffenlarsen]

Looks good overall! One test nit.

[steffenlarsen]

I see this is how we do it in khr/group_interface.hpp too, but would it be more appropriate to guard the definition in sycl/source/feature_test.hpp.in together with all the other feature test macros?

[steffenlarsen]

Nit; Asserts stop execution immediately, so personally I prefer to do something like:

Suggested change

	for (const auto &result : acc)
	assert(result);
	for (const auto &result : acc) {
	if (!result) {
	std::cout << "Failed check_this_nd_item_api check for dimensionality " << Dimensions << ".\n";
	return 1;
	}
	}
	return 0;

and then in the main function you do:

  int Failed = 0;
  // nd_item
  Failed += check_this_nd_item_api<2>();
  Failed += check_this_nd_item_api<2, 3>();
  Failed += check_this_nd_item_api<2, 3, 4>();
  // group
  Failed += check_this_group_api<2>();
  Failed += check_this_group_api<2, 3>();
  Failed += check_this_group_api<2, 3, 4>();
  // sub_group
  Failed += check_this_sub_group_api<2>();
  Failed += check_this_sub_group_api<2, 3>();
  Failed += check_this_sub_group_api<2, 3, 4>();

  return Failed;

The more information, the better.