* Allows creating a GDExtension based 3D Physics Server (for Bullet, PhysX, etc. support)
* Some changes on native struct binding for PhysicsServer
This allows a 3D Physics server created entirely from GDExtension. Once it works, the idea is to port the 2D one to it.
Regression fix, gravity was accumulated between frames after some
changes around area gravity calculation.
Also got rid of unused member and method in soft body class.
Proper logic for changing physics state when disabled and disabled mode
is changed (it was unnecessarily making calls to re-initialize physics).
Extra error handling in soft body implementations to avoid crashes with
invalid mesh.
