Rename structured connectivity index conversion methods

The structured connectivity classes are templated on two tags to determine what 2 incident topological elements are being accessed. Back in the day, these were called the "from" elements and "to" elements, as taken from VTK filter names like PointDataToCellData. However, these names were found to be very confusion, and after much debate they have been renamed to the visit element type and the incident element type. Meaning that a worklet is "visiting" elements of a particular type (such as visiting each cell) and can access "incident" elements of a particular type (such as the points incident on the cell).

I found a few methods converting flat and logical indices using the old, confusing from/to convention. This changes them to the new convention.