Improve performance for manually-specified intersections

[krassowski]

The performance of manually specified intersections is not as good as it could be, and was degraded since #109 (which however, was needed as that fix corrects behaviour and protects users from mis-interpretation of the results). The following lines should be re-written to not generate the full matrix of all possible intersections (all_intersections_matrix) in the first place:

https://github.com/krassowski/complex-upset/blob/a673e50770ac1fc7899b497d8949f25730be854a/R/data.R#L514-L533