gh-38805: use specialized 2-dimensional .log() method in .matrix_on_subgroup()
This should be equivalent but faster (see #38347).
```sage
sage: E = EllipticCurve(GF((2^77-33, 2)), [1,0])
....: P, Q = E.gens()
....: pi = E.automorphisms()[-1]
....: %time pi.matrix_on_subgroup([P, Q])
```
Sage 10.5.beta7:
```
CPU times: user 13.8 s, sys: 32.5 ms, total: 13.8 s
```
This branch:
```
CPU times: user 48.1 ms, sys: 64 µs, total: 48.2 ms
```
URL: https://github.com/sagemath/sage/pull/38805
Reported by: Lorenz Panny
Reviewer(s): grhkm21
