[SYCL] Resolve namespace ambiguity in this_id, this_item, and this_group (#5375)

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_id`,
`sycl::ext::oneapi::experimental::this_item`, and
`sycl::ext::oneapi::experimental::this_group`  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/group.hpp

@@ -439,7 +439,8 @@ namespace oneapi {
 namespace experimental {
 template <int Dims> group<Dims> this_group() {
 #ifdef __SYCL_DEVICE_ONLY__
-  return sycl::detail::Builder::getElement(detail::declptr<group<Dims>>());
+  return sycl::detail::Builder::getElement(
+      sycl::detail::declptr<group<Dims>>());
 #else
   throw sycl::exception(
       sycl::make_error_code(sycl::errc::feature_not_supported),

sycl/include/CL/sycl/id.hpp

@@ -360,7 +360,7 @@ namespace oneapi {
 namespace experimental {
 template <int Dims> id<Dims> this_id() {
 #ifdef __SYCL_DEVICE_ONLY__
-  return sycl::detail::Builder::getElement(detail::declptr<id<Dims>>());
+  return sycl::detail::Builder::getElement(sycl::detail::declptr<id<Dims>>());
 #else
   throw sycl::exception(
       sycl::make_error_code(sycl::errc::feature_not_supported),

sycl/include/CL/sycl/item.hpp

@@ -150,7 +150,7 @@ namespace oneapi {
 namespace experimental {
 template <int Dims> item<Dims> this_item() {
 #ifdef __SYCL_DEVICE_ONLY__
-  return sycl::detail::Builder::getElement(detail::declptr<item<Dims>>());
+  return sycl::detail::Builder::getElement(sycl::detail::declptr<item<Dims>>());
 #else
   throw sycl::exception(
       sycl::make_error_code(sycl::errc::feature_not_supported),