Use enum for loop scan type
Use an enum to specify loop types.
Currently this doesn't remove the use of std::type_index, but that should be possible.
Except:
- In ScurveFitter, Fei4MaskLoop is explicitly used to extract Scap and Lcap. Could this be removed, or does it need a work around?
Another thing to query is the use of LOOP_STYLE_MASK for DC loops. I think this is right as this is what's being done from the analysis point of view.