Add more resize pointers to Rectangle and Ellipse (feature request)

[grofaty]

Pinta/master/github on Ubuntu 20.04.

1. Draw Rectangle and/or Ellipse on canvas.
2. Rectangle Select and/or Ellipse Select.
3. Compare number of resize pointer 1 and 2. Rectangle/Ellipse Select have 8 resize pointers and Rectangle/Ellipse only have 4 resize pointers.

This is feature request add more resize pointers to Rectangle and Ellipse to match Rectangle/Ellipse Select. See attachment.

Why? If I want to resize rectangle only horizontally, the right-middle resize pointers would be handy for precise drawing.