Investigate performance benefits of using sub-group load/store extension

[dmitriy-sobolev]

The deprecated (and non-used) DPC++ extension was removed in #1979, but it worth checking if adoption of the newer extension improves the performance as suggested by @mmichel11 in #1979 (comment).

The new extension is described in SYCL_EXT_ONEAPI_GROUP_LOAD_STORE.