expr/builtin_cast: implement test_cast_as_real & test_cast_as_int (#2218)
expr/builtin_cast: implement test_cast_as_real & test_cast_as_int (#2218)


BusyJay/tikv,pingcap/tikv,c4pt0r/tikv,pingcap/tikv,BusyJay/tikv,BusyJay/tikv,BusyJay/tikv