SIA: Delete last Point of Polygon in drawing mode

[tkwant]

Is your feature request related to a problem? Please describe.
When I am drawing a polygon annotation, and clicked at a wrong position, I cant delete the last Point I added to the polygon.

Describe the solution you'd like
Solution 1: Delete the last Point with undo shortcut
Soluton 2: Delete the lastPoint with mouse Left click or a special key on keyboard.