[SYCL] Resolve namespace ambiguity in this_nd_item (#5258)

Since the `detail` namespace appears in both the `sycl` namespace and in
the `sycl::ext::oneapi::experimental` namespace, the implementation of
`sycl::ext::oneapi::experimental::this_nd_item` may fail due to
`detail::declptr` not existing in the latter. These changes remove the
ambiguity.

Signed-off-by: Steffen Larsen <steffen.larsen@intel.com>

Author: steffenlarsen

sycl/include/CL/sycl/nd_item.hpp

@@ -207,7 +207,8 @@ namespace oneapi {
 namespace experimental {
 template <int Dims> nd_item<Dims> this_nd_item() {
 #ifdef __SYCL_DEVICE_ONLY__
-  return sycl::detail::Builder::getElement(detail::declptr<nd_item<Dims>>());
+  return sycl::detail::Builder::getElement(
+      sycl::detail::declptr<nd_item<Dims>>());
 #else
   throw sycl::exception(
       sycl::make_error_code(sycl::errc::feature_not_supported),

sycl/test/basic_tests/free_function_queries/free_function_queries_interface.cpp

@@ -53,7 +53,7 @@ template <template <int, bool = true> class Item, int Dims> void test() {
       "Wrong return type of free function query for Item");
 }
 
-int main() {
+SYCL_EXTERNAL void test_all() {
   test<sycl::id>(this_id_caller<1>{});
   test<sycl::id>(this_id_caller<2>{});
   test<sycl::id>(this_id_caller<3>{});