Relaxing the restriction of the derived variables to have the same type as the operands

[anagainaru]

For derived operations that do not have the same input and output type, e.g. float sqrt(int)

DerivedData contains now in addition to the data pointer and the start and count Dims, the type of each input operand. The derived functions will have the following signature:

struct DerivedData
{
    void *Data;
    Dims Start;
    Dims Count;
    DataType Type;
};
    std::function<DerivedData(std::vector<DerivedData>, DataType)> ComputeFct;

The second argument DataType is the output type.

[eisenhauer]

Any testing? Or just taking this piece-wise?

(I won't approve yet because you need to turn derived variables back off and when you push a commit to do that it'll dismiss any reviews anyway.)

[anagainaru]

Any testing? Or just taking this piece-wise?

I tested it separately with the POW/SQRT functions that are coming in #4248

I wanted this a separate PR because it creates a backbone for all other functions that need this, not just pow/sqrt (in case we squash merge that one). A slightly complicated way of organizing this, but it made sense at the time.

(I won't approve yet because you need to turn derived variables back off and when you push a commit to do that it'll dismiss any reviews anyway.)

Yes, I'll turn it OFF once I confirm there's no error.