This PR is to add support for the SPIR-V extension SPV_INTEL_bfloat16_conversion (https://github.com/KhronosGroup/SPIRV-Registry/blob/main/extensions/INTEL/SPV_INTEL_bfloat16_conversion.asciidoc) and OpenCL extension cl_intel_bfloat16_conversions (https://registry.khronos.org/OpenCL/extensions/intel/cl_intel_bfloat16_conversions.html).