Shape tools should allow modifying their drawn shapes

[0HyperCube]

Should go hand-in-hand with #2090.

Tools such as the rectangle and shape tool should allow for editing of the created shape.

Tools:

• Line tool adjusting start and end (Allow the Line tool to drag start and end points of line layers #2278)
• Rectangle allowing for moving top left and bottom right corners and ideally for rounding
• Ellipse should allow dragging a handle for the X extent and Y extent and ideally creating an arc/chord
• Spline dragging around points
• Polygon tool handle for the radius and offset of the first vertex. For a star the inner and outer radius should be controlled.

These can be done as separate MRs.