TrkEventCnvTools+TrkEventTPCnv+InDetEventCnvTools+MuonEventCnvTools: MT-friendly version of prepareRIO_OnTrack.

IEventCnvSuperTool::prepareRIO_OnTrack was used to fix up PRD ElementLinks before writing. However, this was done on objects in place, violating const-correctness. This is not MT-safe.

Add a new interface prepareRIO_OnTrackLink. This takes the object as a const pointer and instead of modifying it, returns the new ElementLink components. The T->P converter can then use this to write. Also remove an obsolete use of DataHandle.

Update SurfaceCnv_p2_test to account for new method in IEventCnvSuperTool.