Reshape tool: Shape should be a line instead of a polygon

[fmeier1995]

Describe the issue

A little request: I think it would be better when the shape I draw using reshape tool doesn't close, so it should be a line instead of a polygon (like it is in QGIS using this tool). The "closing line" of the shape has no effect and could be confusing for new users.

Reproduction steps

Steps to reproduce the behavior:

1. Edit a line or a polygon
2. Use reshape tool
3. draw a shape with a few points
   This is what you see before you apply:
   

Expected behavior

I think it is better if it looks like this instead:

or like this: