Is a point on screen inside the element?
Returns true if the screenPosition is contained in this GUIElement. screenPosition is specified in
screen coordinates, like the values returned by the Input.mousePosition property.
If no camera is given a camera filling the entire game window will be assumed.
Note that if the position is inside the element, true will be returned even if
the game object belongs to Ignore Raycast layer (normally mouse events are not sent
to Ignore Raycast objects).
Additional resources: GUILayer.HitTest.