This adds a new `Handles` checkbox to the conversion operator that
affects how the conversion works in the following cases:
`Bezier -> Catmull Rom / Poly / Nurbs` and `Catmull Rom -> Nurbs`.
If enabled, three control points are added for each original control
point, otherwise only one.
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The images show the effect of the toggle. The top result is always the one with handles and the bottom one without.
* `Bezier -> Poly`
* `Bezier -> Catmull Rom`
* `Bezier -> Nurbs`
* `Catmull Rom -> Nurbs`
Pull Request: https://projects.blender.org/blender/blender/pulls/120423
3f2c4db951