FIX: #1195

e.g. for "conventional" https://gdal.org/api/raster_c_api.html#_CPPv424GDALComposeGeoTransformsPKdPKdPd

```
/// The resulting geotransform is the equivalent to padfGT1 and then padfGT2 being applied to a point.
/// Parameters:
///     padfGT1 -- the first geotransform, six values.
///     padfGT2 -- the second geotransform, six values.
///     padfGTOut -- the output geotransform, six values, may safely be the same array as padfGT1 or padfGT2.
void GDALComposeGeoTransforms(const double *padfGeoTransform1, const double *padfGeoTransform2, double *padfGeoTransformOut)
```

Note: `padfGT1` **and then** `padfGT2`, previously we were effectively doing `padfGT2` **and then** `padfGT1`.

I also simplified some of the examples to have more understandable
input/output. I'm not good enough at mental matrix math to know what to
expect from a rotated skew.