Use addSortedForwardStates when inserting new states on TrackEventFitter

propagate and need LHCb!1060 (merged)

not really much faster, just a bit faster in the hlt1 case, states are always already sorted when we are on this function

we call this function only on TrackMasterFitter.cpp:1042

but we have a sort on states just before TrackMasterFitter.cpp:1005

maybe the probability to have 100% of sorted states as input is not true outside hlt1, that's why a specific function as suggested by @sponce

it's not a critical part but maybe still better to avoid duplication of process, difference between these 2 functions is around ~14% according to callgrind