Given the rotation (in radians) and speed calculate the velocity and return it as a vector, or set it to the given vector object. One way to use this is: velocityFromRotation(rotation, 200, sprite.body.velocity) which will set the values directly to the sprite's velocity and not create a new vector object.
The angle in radians.
The speed it will move, in pixels per second squared
The Vector2 in which the x and y properties will be set to the calculated velocity.
The Vector2 that stores the velocity.