TriggerTest: Use TriggerValidation MC prescale set for all full-menu MC tests

Change menu name from LS2_v1 to LS2_v1_TriggerValidation_mc_prescale for all TriggerTest tests which run on MC inputs and use the full LS2_v1 menu. This means that slice tests and L1SimOnly tests are excluded from this change.

This disables some CPU-hungry chains in these tests, as requested in ATR-21613