ManifoldSubset.intersection: Compute more supersets

[mkoeppe]

self.intersection(other) should be a subset of any self_superset.intersection(other_superset).

This will be useful in particular if some pair self_superset, other_superset is known to be disjoint.

This could also provide another test for Point.__eq__: if the parents of the points have an empty intersection, the points must be unequal. (I don't know how useful this is.)

Checking an antichain of self_supersets against an antichain of other_supersets takes quadratic time. But speed ups for chains are possible by convolution/binary search.

CC: @egourgoulhon @mjungmath @tscrim

Component: manifolds

Issue created by migration from https://trac.sagemath.org/ticket/31738