new Phase2TrackerCluster1D dataformat

That dataformat is designed to represent 1D clusters, as found in strips.
Compared to the SiStripCluster, there is no need to track strip charges, which makes the barycenter calculation simpler.
Also, the reference point (beginning) is a 2D digi for phase2.
New Phase2TrackerCluster2D dataformat

Phase2TrackerCluster2D are representing a 2D cluster made of digital digi.
Each cluster is defined by its anchor point (a digi) and a set of 2D offsets.
It has a size, and a position.
new Phase2TrackerStub dataformat

This simple dataformat is to hold the stubs as they come from the hardware.
Therefore, it has no reference to sim objects, nor direct links to digis or clusters.