Voxel demo doesn't scale acceleration or friction by delta

[furrykef]

Which demo project is affected:
godot-demo-projects/3d/voxel

OS/device including version:
any

Issue description:
In player/player.gd, constants such as MOVEMENT_SPEED_GROUND and MOVEMENT_FRICTION_GROUND are multiplied without being scaled by delta (e.g., here). That means the amount of acceleration or friction will be dependent on the physics time step. The player character will accelerate twice as fast at 120 ticks per second than at 60, for example.

The correct way to do it is to multiply by MOVEMENT_SPEED_GROUND**delta, etc. (notice that delta is an exponent). This will require changing the constants to reflect the scaling; since the project's physics time step is currently set to 120 ticks per second, the constants would have to be multiplied by 120 to give the same behavior.

[Calinou]

Feel free to open a pull request for this 🙂

See also godotengine/godot-proposals#9803.