[Spec change] Add x, y, and z shorthands to id and range classes

Please review whether https://github.com/KhronosGroup/SYCL-Docs/pull/679 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.

Start by reviewing SYCL-Docs pull request 679 and compare its proposed id and range shorthand changes with the SYCL-CTS coverage. No CTS files or tests are named, so locate the relevant conformance tests after understanding the specification change. Done means either opening and linking a CTS PR for required changes or closing this issue when no changes are needed.

Written by the indexing model from the issue text.