qtquick: Fix DND operation never ending

When double-clicking a title bar we're getting: Press, Release,
Press and never the Release. We get the MouseDblClickEvent instead,
so handle that

src/private/DragController.cpp

@@ -165,6 +165,15 @@ bool StatePreDrag::handleMouseButtonRelease(QPoint)
     return false;
 }
 
+bool StatePreDrag::handleMouseDoubleClick()
+{
+    // This is only needed for QtQuick.
+    // With QtQuick, when double clicking, we get: Press, Release, Press, Double-click. and never
+    // receive the last Release event.
+    Q_EMIT q->dragCanceled();
+    return false;
+}
+
 StateDragging::StateDragging(DragController *parent)
     : StateBase(parent)
 {
@@ -296,6 +305,14 @@ bool StateDragging::handleMouseMove(QPoint globalPos)
     return true;
 }
 
+bool StateDragging::handleMouseDoubleClick()
+{
+    // See comment in StatePreDrag::handleMouseDoubleClick().
+    // Very unlikely that we're in this state though, due to manhattan length
+    Q_EMIT q->dragCanceled();
+    return false;
+}
+
 StateDraggingWayland::StateDraggingWayland(DragController *parent)
     : StateDragging(parent)
 {
@@ -486,6 +503,7 @@ static QMouseEvent *mouseEvent(QEvent *e)
 {
     switch (e->type()) {
     case QEvent::MouseButtonPress:
+    case QEvent::MouseButtonDblClick:
     case QEvent::MouseButtonRelease:
     case QEvent::MouseMove:
     case QEvent::NonClientAreaMouseButtonPress:
@@ -567,6 +585,8 @@ bool DragController::eventFilter(QObject *o, QEvent *e)
     case QEvent::NonClientAreaMouseMove:
     case QEvent::MouseMove:
         return activeState()->handleMouseMove(Qt5Qt6Compat::eventGlobalPos(me));
+    case QEvent::MouseButtonDblClick:
+        return activeState()->handleMouseDoubleClick();
     default:
         break;
     }

src/private/DragController_p.h

@@ -106,6 +106,7 @@ public:
     virtual bool handleMouseButtonPress(Draggable * /*receiver*/, QPoint /*globalPos*/, QPoint /*pos*/) { return false; }
     virtual bool handleMouseMove(QPoint /*globalPos*/) { return false; }
     virtual bool handleMouseButtonRelease(QPoint /*globalPos*/) { return false; }
+    virtual bool handleMouseDoubleClick() { return false; }
 
     // Only interesting for Wayland
     virtual bool handleDragEnter(QDragEnterEvent *, DropArea *) { return false; }
@@ -138,6 +139,7 @@ public:
     void onEntry(QEvent *) override;
     bool handleMouseMove(QPoint globalPos) override;
     bool handleMouseButtonRelease(QPoint) override;
+    bool handleMouseDoubleClick() override;
 };
 
 // Used on all platforms except Wayland. @see StateDraggingWayland
@@ -150,6 +152,7 @@ public:
     void onEntry(QEvent *) override;
     bool handleMouseButtonRelease(QPoint globalPos) override;
     bool handleMouseMove(QPoint globalPos) override;
+    bool handleMouseDoubleClick() override;
 };
 
 // Used on wayland only to use QDrag instead of setting geometry on mouse-move.

src/private/quick/TitleBarQuick.cpp

@@ -46,6 +46,7 @@ void TitleBarQuick::filterEvents(QObject *obj)
 bool TitleBarQuick::eventFilter(QObject *, QEvent *ev)
 {
     switch (ev->type()) {
+    case QEvent::MouseButtonDblClick:
     case QEvent::MouseButtonPress:
     case QEvent::MouseButtonRelease:
     case QEvent::MouseMove: