Add support for 1Translation+ 1Rotation 2d Joint

[Selus]

Right now it's not possible to implement a groove joint that Godot uses.

Detailed info in:
appsinacup/godot-rapier-physics#317

[ThierryBerger]

Thanks for the issue ; I'm surprised about the ¨GrooveJoint" naming, so I'd like to clear that up:

Strictly speaking, a groove joint seems to refer to a constraint allowing only translation on 1 axis, but here we're discussing 1 translation + 1 rotation.

This "specific" (rotation) behaviour seems to come from godot. Their documentation isn't clear on whether that rotation is intended 🤔. If we're copying godot behaviour, I'd like to clear that up.

The linked issue is clear though that godot implementation allows for rotation.

To me, this kind of joint seems more similar to a PinSlot, would it make more sense as a name, to allow for a 3d PinSlot in the future ?

[Ughuuu]

Can this now be closed? The PinSlotJoint PR has been merged