22.0-cleanup-TRT_DetElementsRoadTool_xk

Work undertaken in the context of ATLASRECTS-5936 (Item 2 of the first comment), clarifying pointer ownership for TrackParameters pointers. Incidental cleanups also introduced (using cmath functions, variable names made more explanatory, use ATH_CHECK). Subsequent changes in this direction will need changes to the interface, not done in this MR.