putSlot method
Implementation
@protected
int putSlot(int entityIndex) {
final existing = denseIndexOf(entityIndex);
if (existing >= 0) return existing;
_ensureSparse(entityIndex);
final dense = _length;
_ensureDense(dense + 1);
_denseEntities[dense] = entityIndex;
_sparse[entityIndex] = dense + 1;
_length = dense + 1;
return dense;
}