"Save image" should save as shown in the notebook, including background

[minsa110]

Feedback from PyCon 2022

"The "save image" button saves my image with transparent background so I can barely see my axes and title."

In the notebook (and as expected to be saved):

When I open the saved file:

(If you look closely, you can see the axes.. It's just black and the background of my dark themed machine is very dark grey...)

[greazer]

@minsa110, we discussed this for a few minutes. Overall, we don't think it's safe to override the transparency of the plot image. We are plotting on top of a white rectangle.

This could also be addressed if/when core supports copying images to clipboard.