changed data type enumeration to a enumeration class

the No_DataType enumerator was replaced with DataType{} (to indicate an
unset data type; all Xx_DataType were renamed without the _DataType and
uses changed to DataType::Xx; the DataType::Double was assigned to one
so as not to conflict with the value of DataType{}; and the test names
awk script was modified to look for the data type enum class and
generate an unordered map for data type to string with an initializer
list instead of C style array of character array