TransientPropagation: Gain Needs to Generate Carriers

When calculating the cumulative gain, we up to now completely forgot to also generate the opposite carrier type. This MR makes it possible to call the propagate method recursively and generates carriers of the opposite type whenever the cumulative gain crosses an integer threshold, and uses the current local position and time for the new carriers.

Line graphs correctly represent these carriers.

All these carriers are linked to the same initial DepositedCharge but generate their own final-state PropagatedCharge.