Optimize half conversion for SYCL kernel
## Motivation:
Add support for SYCL half implicit/explicit conversion in SYCL kernels.
## Additional Context:
Macro `SYCL_LANGUAGE_VERSION` is suggested by SYCL compiler to instead of `__SYCL_DEVICE_ONLY__` in current version unless device and host specific implementation of the same function is necessary.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76515
Approved by: https://github.com/ezyang
