CV Quad Warp

Applies the homography defined by 4 annotated corner points. 'extract' rectifies the quad into a rectangle with the TRUE aspect ratio recovered from the perspective (a manual document scan; Zhang's whiteboard method with the principal point at the image center); 'fill' warps THIS image into the quad on a canvas (poster / billboard / screen replacement). The 4 points may arrive in any order - 'CV Annotate Points' click order, detections, ... - they are sorted TL/TR/BR/BL automatically. The matrix output is the 3x3 homography actually used, ready for 'CV Homography Map' to combine with other remap distortions. Failure-tolerant: anything other than exactly 4 points passes the image through with success=false and an identity matrix - branch on success with an if/else node.