Add DV-track variables to SUSY15
requested to merge atlas-phys-susy-wg/RPVLL/DisplacedVertices/athena:21.2-tmp-susy15-changes into 21.2
This MR will add DV-track variables to SUSY15 derivations. When the secondary vertexing algorithm is re-run in the derivation step, tracks which are included in DVs are decorated with additional information, for example pT, eta, and phi with respect to the DV position. These new track decorations have a unique suffix which matches the suffix of the new DV container.