tilt property Null safety
For PointerDeviceKind.stylus and PointerDeviceKind.invertedStylus events:
The angle of the stylus, in radians in the range:
0 <= tilt <= pi/2
...giving the angle of the axis of the stylus, relative to the axis perpendicular to the input surface (thus 0.0 indicates the stylus is orthogonal to the plane of the input surface, while pi/2 indicates that the stylus is flat on that surface).
final double tilt;