Fix documentation for get_velocity_at_local_position

[ghsoares]

Resolves godotengine/godot-docs#7110

There is a misleading description of the expected space of local_position parameter of get_velocity_at_local_position function of both PhysicsDirectBodyState2D and PhysicsDirectBodyState3D classes.

See the docs issue, but briefly, by passing an vector in local space of the body (both translation and rotation), gives incorrect values, by passing an vector in local translation, but global rotation (meaning an offset product of global_point - body.transform.origin) it returns the correct velocity value in global space.

The function has the same behaviour of apply_force for the parameter, expecting an vector in local translation space, but global rotation space.

It's ideal to rename the function to something like get_velocity_at_offset, but this goes outside the scope of this PR and the docs update is more urgent.

[Repiteo]

Thanks! Congratulations on your first merged contribution! 🎉