[BUG] ACPC in surface RAS, should be in Scanner RAS

[alexrockhill]

I realized that in https://mne.tools/mne-bids/dev/auto_examples/convert_ieeg_to_bids.html the ACPC coordinates are in surface RAS but in https://mne.tools/stable/auto_tutorials/clinical/10_ieeg_localize.html we tell users (correctly) to align scanner RAS to ACPC. I can make a PR, it might be nice to use the Freesurfer T1 in a convenience function that converts a montage to scanner RAS. Although someone could share a T1 that isn't 256 x 256 x 256 and then the Freesurfer T1 wouldn't be the same size, but, I think, since RAS is in mm/m, it should be compensated for by the affine and should be fine to use the Freesurfer T1 even in that instance.