Calculating max common subpattern does not support structure intersection

[shimon77]

The Multi Pattern Graph implements the algorithm for maximal common subpattern according to Appendix A in the article:
https://assaf.net.technion.ac.il/files/2019/03/Real-Time-Multi-Pattern-Detection-over-Event-Streams.pdf

After intersecting the events and the conditions, there needs to be a structure intersection as well.
Currently this is not supported, and instead we simply check for structure equivalence (otherwise we do not share the subpattern at all).