[Spec change] Add sycl_khr_free_function_commands extension

[sycl-issue-bot]

Please review whether KhronosGroup/SYCL-Docs#644 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]

The sycl_khr_free_function_commands extension is an evolution of the sycl_ext_oneapi_enqueue_functions extension, which already has some tests in the CTS here.

The sycl_khr_free_function_commands tests can re-use a lot of this code, but some changes will be required:

• Some names are changed (e.g., submit_with_event becomes submit_tracked, nd_launch becomes launch_grouped).
• There is a new invocation class that will require tests for its member functions.