As listed in #7368, we should be able to compose isogenies.
See also discussions in #12880, comments 20 and 21.

Depends on #12880

CC: @defeo @JohnCremona @pjbruin

Component: elliptic curves

Author: Sébastien Besnier

Branch/Commit: 308157e

Reviewer: Peter Bruin

Issue created by migration from https://trac.sagemath.org/ticket/16245