Add a new p2 persistent version of sTGC PrepData

sTGC PrepData format wrongly assumes that the local y-coordinate of readout elements is zero. It is correct for strips and wiregroups, but not for pads. Position of sTGC pads is defined using both x- and y-coordinates. This MR adds a new _p2 persistent version of the sTGC PrepData that has the local y-coordinate, and the associated transient-persistent converters. Therefore, changes related to pad position are expected.

Thanks the offline DAQ team (@sfuenzal @makbiyik @carquin) for spotting this issue.