(PR) feat: Double tap and drag to erase

saber-notes#1118

Signed-off-by: AnErrupTion <anerruption@disroot.org>

Author: AnErrupTion

lib/components/canvas/canvas_gesture_detector.dart

@@ -479,6 +479,8 @@ class CanvasGestureDetectorState extends State<CanvasGestureDetector> {
           onPointerUp: _listenerPointerUpEvent,
           onPointerHover: _listenerPointerHoverEvent,
           child: GestureDetector(
+	          // Double tap and drag to switch to eraser
+	          onDoubleTapDown: (details) => widget.onStylusButtonChanged(true),
             child: LayoutBuilder(
               builder: (BuildContext context, BoxConstraints containerBounds) {
                 this.containerBounds = containerBounds;