Depending on compilation flags, applying a transform used to either:
- work;
- fail throwing an abstract method not implemented message;
- fail silently.
Now it should consistently work, like the other geometries.
Adding a polygon factory method creating an approximation of a circle on
a plane would be useful for users wanting the circle to be deformed.
It would be similar to the `circular` function which creates an
approximation of a circle on a sphere.
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