Improve Doxygen configuration for hiding implementation details of SYCL API

It is not sufficient. Some support from preprocessor will be needed.
Use Doxygen pre-processing to hide implementation detail for the SYCL API

When TRISYCL_HIDE_IMPLEMENTATION is defined, remove the content of
TRISYCL_IMPL(...)
Hide internal operations on range<> from the SYCL API documentation
Remove unused code from implementation