We define a subclass of ManifoldSubset, instances of which represent the image of a continuous map.

In particular, this will allow an embedded submanifold to be considered as a subset of the ambient manifold.

CC: @egourgoulhon @tscrim @yuan-zhou @mjungmath @mwageringel @roed314

Component: manifolds

Author: Matthias Koeppe

Branch/Commit: 0f3e36d

Reviewer: Eric Gourgoulhon, Michael Jung

Issue created by migration from https://trac.sagemath.org/ticket/31653