Display visual feedback of where cards will go (#5737)

This is part of the code from #4974, including an improved drag-and-drop
API and its use to display visual feedback of card destination on the
board.

It does not include the improved logic for pushing cards around as I
still need to figure out edge cases there - the logic for choosing where
cards go is not changed, so some of the artifacts described in #4817
and #4975 (particularly around multi-card) are still present.

cockatrice/src/game/zones/table_zone.h

@@ -77,6 +77,8 @@ private:
      */
     bool active;
 
+    QGraphicsPathItem *m_feedbackItem = nullptr;
+
     bool isInverted() const;
 
 private slots:
@@ -118,6 +120,14 @@ public:
      */
     void toggleTapped();
 
+    bool dragEnter(CardDragItem *dragItem, const QPointF &pos) override;
+
+    void dragMove(CardDragItem *dragItem, const QPointF &pos) override;
+
+    void dragAccept(CardDragItem *dragItem, const QPointF &pos) override;
+
+    void dragLeave(CardDragItem *dragItem) override;
+
     /**
        See HandleDropEventByGrid
      */
@@ -133,13 +143,6 @@ public:
      */
     CardItem *getCardFromGrid(const QPoint &gridPoint) const;
 
-    /**
-       @return CardItem from coordinate location
-     */
-    CardItem *getCardFromCoords(const QPointF &point) const;
-
-    QPointF closestGridPoint(const QPointF &point) override;
-
     static int clampValidTableRow(const int row);
 
     /**
@@ -184,6 +187,8 @@ private:
     void paintZoneOutline(QPainter *painter);
     void paintLandDivider(QPainter *painter);
 
+    void updateFeedback(CardDragItem *dragItem, const QPointF &point);
+
     /*
     Calculates card stack widths so mapping functions work properly
     */