[ENH]: Fix aspect ratio for zoom box with 'ctrl' key.

[scottshambaugh]

Problem

When zooming in with the toolbar box select, you can constrain the zoom to the 'x' or 'y' directions by pressing those keys. It would be great if you could enforce an equal aspect ratio for the selection box, which to follow the convention of the pan tool would be done with the 'ctrl'/'control' key as a modifier. This should roll in on 2D and 3D plots.

Proposed solution

No response