Refactor : ComplexApiDataType - remove properties on the super type that are not common

[amorton]

Class has

public abstract class ComplexApiDataType implements ApiDataType {
  private final String apiName;
  private final PrimitiveApiDataType keyType;
  private final PrimitiveApiDataType valueType;
  private final int dimension;

Only the valueType is common to all subclasses of complex type, we should move the other properties down to the sub classes.

While here, can we also cache the CQLType returned in

  public DataType getCqlType() {
      return DataTypes.mapOf(
          ApiDataTypeDefs.from(getKeyType()).get().getCqlType(),
          ApiDataTypeDefs.from(getValueType()).get().getCqlType());
    }

(it also uses apiName as a string, we will fix that later I think)