[Spec change] Add sycl_khr_work_item_queries extension

[sycl-issue-bot]

Please review whether KhronosGroup/SYCL-Docs#682 by @Pennycook requires any changes to the CTS.

If changes are required: Open a new PR addressing the changes and link it to this issue.
If no changes are required: Close this issue and proceed with the spec PR.

[Pennycook]

This change will require CTS changes.

Since these queries return instances of existing classes, it is probably sufficient to just test for equality:

q.parallel_for(sycl::nd_range<1>{1024}, [=](sycl::nd_item<1> it) {
  result[it.global_linear_id(0)] = (sycl::khr::this_work_item::get_nd_item<1>() == it);
});

...with equality tests for sycl::nd_item, sycl::group and sycl::sub_group, in one-, two- and three-dimensional kernels.

We don't have to test cases where the number of dimensions in the query don't match the number of dimensions in the kernel launch, because the behavior in that case is undefined.