gh-37940: Support morphisms in `Matroid` constructor
This follows the merging of #37692 and it enables the (re-)feeding of a
linear matroid's morphism representation into the `Matroid` constructor.
Example:
```
sage: M = matroids.catalog.Fano()
sage: A = M.representation(order=True); A
Generic morphism:
From: Free module generated by {'a', 'b', 'c', 'd', 'e', 'f', 'g'}
over Finite Field of size 2
To: Free module generated by {0, 1, 2} over Finite Field of size 2
sage: Matroid(A)
Binary matroid of rank 3 on 7 elements, type (3, 0)
```
URL: https://github.com/sagemath/sage/pull/37940
Reported by: gmou3
Reviewer(s): gmou3, Matthias Köppe, Travis Scrimshaw
