Copying and Filling Zero Bytes

### Specification Version

SYCL 2020 (Revision 9)

### Section Number(s)

https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#subsec:explicitmemory

### Issue Description

Found while working on the "unified SVM" OpenCL extension: https://github.com/KhronosGroup/OpenCL-Docs/pull/1282:

https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#subsec:explicitmemory

Is "zero bytes" valid for all of the "SYCL functions for explicit memory operations" - things like copy(), fill(), memcpy(), memset()?

If a size of zero is valid, is any validation done on any of the pointer arguments, or may they be NULL or otherwise bogus?

Note: I took a quick pass through the SYCL CTS and I don't think any of these scenarios are tested, so if they are valid then we may want CTS enhancements as well.

Thanks!

### Code Example (Optional)

_No response_

Start with the SYCL 2020 explicit memory operations section and compare the related OpenCL-Docs pull request #1282. Review the SYCL CTS coverage for copy(), fill(), memcpy(), and memset(); done means the specification answers zero-byte and pointer-validation behavior, with CTS enhancements identified if required.

Written by the indexing model from the issue text.