rel_quad_to
Description:
Adds a [quadratic Bézier curve](https://en.
wikipedia.org/wiki/B%C3a9zier_curve) from the current point to x2, y2 with x1
      , y1 the control point.
All coordinates are given relative to the current point.
This is the relative version of [method@Gsk.PathBuilder.quad_to].
Parameters:
| this | 
           a path builder  | 
      
| x1 | 
           x offset of control point  | 
      
| y1 | 
           y offset of control point  | 
      
| x2 | 
           x offset of the end of the curve  | 
      
| y2 | 
           y offset of the end of the curve  |