gh-38347: support passing two base points to .log() for elliptic-curve points
The points on an elliptic curve over a finite field form a group of rank
up to $2$. In this patch we add support for passing two base points
instead of just one to the `.log()` method, which will decompose the
given point as a linear combination of the given points. This
functionality is already available via the `.abelian_group()` method of
the elliptic curve, but the latter is much slower since it relies only
on generic-group algorithms and does not exploit the Weil pairing:
```
sage: F = GF((5, 60), 'a')
sage: E = EllipticCurve(F, [1, 1])
sage: A = E.abelian_group()
sage: P, Q = E.gens()[::-1]
sage: T = randrange(P.order()) * P + randrange(Q.order()) * Q
sage: %time A.discrete_log(T, [P,Q])
CPU times: user 47.4 s, sys: 74 ms, total: 47.5 s
Wall time: 47.6 s
(2474, 185989333112663415489036252299763200191)
sage: %time T.log([P, Q])
CPU times: user 1.43 s, sys: 3.34 ms, total: 1.44 s
Wall time: 1.44 s
(2474, 185989333112663415489036252299763200191)
```
### ⌛ Dependencies
- #38350
URL: https://github.com/sagemath/sage/pull/38347
Reported by: Lorenz Panny
Reviewer(s): Giacomo Pope, Lorenz Panny
