Synchronizes different input streams (e.g. for visualizations).
It has a similar to Union operator but sends its output to a corresponding output port, e.g. if the element comes over port 0 the output will be send to port 0, if the element comes over port 1 the element will be send to port 1. The operator conserves order, i.e. no element is written to any port, if there could be an older element from other input ports.
output = SYNCHRONIZE(left, right)