Add flag in ParticleCombiner to allow different algorithm inputs for children with the same ID

Currently it is not supported to have different algorithm inputs for continuous children with the same PID. However this can be an issue for long-lived particles, when one candidate is reconstructed from long tracks and the other one is reconstructed from downstream tracks (see for example Moore!1249 (merged))

Here I try to fix the issue, enabling this possibility for a limited number of predefined particles (thanks to @mstahl for the suggestion). @mvesteri @poluekt @nnolte @rmatev can this be a viable solution?

cc @lpica