No device-specific kernel information descriptor for local memory

The SYCL specification, in table 138 in [§4.11.13.2](https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#_kernel_information_descriptors), defines a device-specific kernel information descriptor `info::kernel_device_specific::private_mem_size` to query for the private memory used by each work-item. This matches OpenCL's [`CL_KERNEL_PRIVATE_MEM_SIZE`](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#CL_KERNEL_PRIVATE_MEM_SIZE).

OpenCL also defines [`CL_KERNEL_LOCAL_MEM_SIZE`](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#CL_KERNEL_LOCAL_MEM_SIZE) to query for the local memory used by a kernel, but SYCL does not define an equivalent device-specific kernel information descriptor (e.g., `info::kernel_device_specific::local_mem_size`). This could be useful to users, especially if local memory was used by builtins, e.g., for reduction.

Was this left out on purpose or was this an oversight and should be added?

Start with table 138 in §4.11.13.2 of the SYCL specification and compare it with OpenCL's CL_KERNEL_LOCAL_MEM_SIZE descriptor. Determine whether a device-specific local-memory descriptor should be added and document the decision and resulting specification change.

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