[SYCL] Kernel ID lookup should fail at link-time

The current design of the kernel name resolution in the SYCL integration header only makes kernel names visible within the same TU. This means that kernel IDs cannot be created for kernels in other TUs, while `get_kernel_id()` and `has_kernel()` should fail at link-time.

As mentioned by @gmlueck in https://github.com/intel/llvm/pull/8070#discussion_r1088961081 a solution is to have the integration header specialize `get_kernel_id()` or change the kernel name resolution from being part of `KernelInfo` to a non-constexpr function declaration specialized by the integration header.

See discussion: https://github.com/intel/llvm/pull/8070#discussion_r1087935797