Activate the next-to-next bunch digitization for the 4-bunch trigger-data readout

Since Run-3, the trigger readout of the L1Muon Endcap system has been updated to the 4-bunch readout (previous, current, next, and next-to-next). The update of Digitization is needed to follow the same feature in MC.

The next-to-next bunch BCtag is defined in !55480 (merged). This MR implements the BC tagging of the next-to-next bunch at the digitization phase. This change does not see an effect on the normal muons, but dramatically affects the BC tag distribution of slow-particles.