Add operation information to the derived comp function

[anagainaru]

Operations can have one or several of the following information attached:

struct OpInfo
{
    adios2::detail::ExpressionOperator operation;
    std::vector<std::tuple<size_t, size_t, size_t>> indices;
    double constant; 
};

The functions that compute a derive variable or that return the dimensions of a derived variable do not take any of this information.

struct OperatorFunctions
{
    std::function<DerivedData(std::vector<DerivedData>, DataType)> ComputeFct;
    std::function<Dims(std::vector<Dims>)> DimsFct;
};

• We might need a function to return the type of the derived variable.