[UR] Unify reference counting helpers across adapters

[npmiller]

Every adapter (except OpenCL) has their own reference counting helper class or interface, it would be good to create a common UR reference counting interface and share that across all adapters:

• Native CPU: https://github.com/intel/llvm/blob/sycl/unified-runtime/source/adapters/native_cpu/common.hpp#L47
• L0: https://github.com/intel/llvm/blob/sycl/unified-runtime/source/adapters/level_zero/common.hpp#L225
• CUDA: https://github.com/intel/llvm/blob/sycl/unified-runtime/source/adapters/cuda/event.hpp#L68
• HIP: https://github.com/intel/llvm/blob/sycl/unified-runtime/source/adapters/hip/event.hpp#L64