SYCL: Introduce RegisterFileSize

[masterleinad]

Similar to https://github.com/kokkos/kokkos/pull/6496, this pull request introduces a new policy property called RegisterFileSize that allows forcing the register file size to small or large for Intel GPUs with the SYCL backend. See https://www.intel.com/content/www/us/en/docs/oneapi/optimization-guide-gpu/2024-1/porting-registers.html for some cases here setting this to different values makes a measurable difference. The implementation is based on an extension described in https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/experimental/sycl_ext_intel_grf_size.asciidoc.

Based on top of #6496.