BUG: Butterfly mode scale bars overlap

[larsoner]

On latest MNE main (so you can use --butterfly) you can see:

MNE_BROWSER_BACKEND=matplotlib mne browse_raw ~/mne_data/MNE-sample-data/MEG/sample/sample_audvis_raw.fif --butterfly --clipping None

matplotlib	qt

BUG 1: If you plot in non-butterfly mode then hit "b" you get a different scale bar (e.g., 800 fT/cm instead of 400 fT/cm):

BUG 2: I think the spacing might also be off -- there is too much space at the top and bottom of the plot compared to the MPL version (which seems more correct). Some of these differences probably give rise to these differences in the MNE-Python test:

https://github.com/mne-tools/mne-python/pull/12721/files#diff-54ae16f8e47e25048ec09729d5f2175a49995177d97d1c0349bab066cbc90fffR1243-R1244

BUG 3: The z order is wrong. Whichever channel type is at the top should have the highest z order probably (it comes earlier in the data order so should be considered higher priority I think).