* revise atan op * use parametrized vistor API * use new gtest macros * Update docs/ops/arithmetic/Atan_1.md Co-authored-by: Gabriele Galiero Casay <gabriele.galiero.casay@intel.com> * Update docs/ops/arithmetic/Atan_1.md Co-authored-by: Gabriele Galiero Casay <gabriele.galiero.casay@intel.com> * Update ngraph/core/src/op/atan.cpp Co-authored-by: Gabriele Galiero Casay <gabriele.galiero.casay@intel.com> * update doc to follow the rules * create type_prop for atan * drop op_eval to be covered in backend * add the missing type prop case * add integer type ref impl * fix clang issue Co-authored-by: Gabriele Galiero Casay <gabriele.galiero.casay@intel.com>