Add sycl::ext::oneapi::experimental::printf to the supported extensions list

[dvrogozh]

The sycl::ext::oneapi::experimental::printf is currently experimental extension heavily used in the projects with SYCL kernels such as Pytorch for debug.

• Documentation for this extension seems missing in https://github.com/intel/llvm/tree/sycl/sycl/doc. Can it be added?
• Can this extension be promoted from experimental to supported?

See: https://github.com/intel/torch-xpu-ops/blob/9022a83389905509033d02cda8005c21be9c976c/src/comm/SYCLHelpers.h#L347

CC: @gmlueck, @EikanWang, @guangyey

[gmlueck]

There are many problems with the existing sycl::ext::oneapi::experimental::printf. We are using the internal tracker CMPLRLLVM-73975 to collect requirements and track implementation of a more robust "printf".

We have already discussed this in the Khronos WG, and members are strongly in favor of defining a KHR for this feature.