buildEventHolders
Builds a holder for every entry in this list via buildEventHolder — the standard way a TileHolderBuilder/EventHolderBuilder turns its own schema's events field into the events constructor argument of the Holder it's building.
Receiver
the schema's own declared events, or null if it declares none.
Return
a mutable list of built holders, in the same order — empty (not null) when the receiver is null, so callers never need a separate null-check on the result.