[SYCL] Add test for free function kernels extension that checks emitted diagnostics if kernel violates restrictions (#17954)
This PR adds test for free function kernels extension that checks
emitted diagnostics if kernel violates restrictions specified in spec
for declaration of free function kernel.
https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/proposed/sycl_ext_oneapi_free_function_kernels.asciidoc#defining-a-free-function-kernel
Test introduced based on test plan:
https://github.com/intel/llvm/pull/17886