Using the margin property to create rounded shapes

[Demindiro]

This video shows that the margin property can be abused to create rounded shapes in Bullet: https://www.youtube.com/watch?v=BGAwRKPlpCw&t=367s

Since Rapier3D doesn't have a margin property for its shapes but it does have rounded shapes, we could use this to indirectly implement rounded shapes.

The only caveats are:

• The default collision margin in Godot is 0.04, which means every shape is rounded by default. This can have unintended side effects
• The inspector doesn't allow setting the margin to lower than 0.001, so the threshold should be ~0.0010001 instead of just 0.

[Demindiro]

Reading the Bullet manual (https://raw.githubusercontent.com/bulletphysics/bullet3/master/docs/Bullet_User_Manual.pdf) it seems that the margin trick doesn't work for all shapes, such as boxes, because Bullet compensates for the gap it would create normally (see page 15 "Collision Margin").