ENH: Allow mne coreg to adjust other dataset properties for OPM data

[larsoner]

For OPM data, it would be convenient to allow mne coreg to adjust more than just the head_mri_t (by writing -trans.fif files, which it does currently).

Even with our existing OPM dataset from years ago, the head and MRI coordinate frames are taken as equal, which they shouldn't be. We should allow for using the current (in the GUI) sensor<->MRI relationship and use the current LPA/Nasion/RPA (from the MRI) to correct the LPA/Nasion/RPA in info['dig'], which in turn should update the head coordinate frame definition, which in turn should change the rest of info['dig'], info['chs][ii]['loc'], info['dev_head_t'], etc.

Adapted from #11405

[larsoner]

... as part of this, we probably will want to add the ability to tell ICP fitting to use the MEG sensor locations as if they were digitization points as well.