Updated OperatorUtility to avoid C2672 and C2783 (#9651)
Updated OperatorUtility to avoid compiler error errors C2672 and C2783.
- Error C2672: 'TryMapStringToIndex': no matching overloaded function found
- Error C2783: 'std::optional<_Ty> Dml::TryMapStringToIndex(std::string_view,gsl::span<const Dml::NameAndIndex>)': could not deduce template argument for 'T'. note: see declaration of 'Dml::TryMapStringToIndex'. 'TryMapStringToIndex': function declaration must be available as none of the arguments depend on a template parameter
