Rewrite broadcast/broadcast! over a pair of (input) sparse matrices with new (#19372) semantics / less pessimistic allocation behavior and optimize a few inefficiently handled common cases. Also provide a broadcast/broadcast! implementation capable of (relatively) efficiently handling an arbitrary number of (input) sparse matrices. Integrate with the map/map! implementation, and touch up a few rough edges of the map/map! implementation. Test.

Author: Sacha0