Rewrite addon to rust/gdext

[Ughuuu]

As of now, the addon has parts in c++ and a wrapper in rust.
Because of this, it's hard to make web builds work (because of the first wrapper in rust, it needs some js hacks to work).
GDext(godot-rust) extension somehow figured it out. It might be difficult to do here.
Also, cross platform determinism is way easier to do in rust than in c++.

That being said, I think it would be most beneficial to have all the code written in rust, and not have 2 layers of code(c++ and rust).

[Ughuuu]

Initial draft(1 to 1 transcribe). After this a test phase should happen.

Progress:

• Bodies: Rapier Area
• Bodies: Rapier Body
• Bodies: Rapier Collision Object
• Bodies: Rapier Direct Body Space
• Fluids: Fluid Effect
• Fluids: Rapier Fluid
• Joints: Rapier Damped Spring Joint
• Joints: Rapier Groove Joint
• Joints: Rapier Joint
• Joints: Rapier Pin Joint
• Rapier2D: Wrapper
• Servers: Body Utils
• Servers: Rapier Physics Server
• Servers: Rapier Project Settings
• Servers: Rapier Physics Singleton
• Shapes: Rapier Capsule Shape
• Shapes: Rapier Circle Shape
• Shapes: Rapier Concave Polygon Shape
• Shapes: Rapier Convex Polygon Shape
• Shapes: Rapier Rectangle Shape
• Shapes: Rapier Segment Shape
• Shapes: Rapier Separation Ray Shape
• Shapes: Rapier World Boundary Shape
• Shapes: Rapier Shape
• Spaces: Rapier Direct Space State
• Spaces: Rapier Space

[Ughuuu]

Functionality implementation is done, now the tests have to pass:

• 44/44: Rigidbody
• 1/2: CollisionShape
• 5/5: Raycast
• 47/48: DirectSpaceState
• 18/20: CharacterBody
• 18/21: Area
• 4/10: Moving Platforms

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• 137/150: Total tests