Windows QPA: Fix sending of the mouse release in case of a Drop

Use the new API of QWindowSystemInterface to send the release
event which does not depend on the state of
QGuiApplicationPrivate::mouse_buttons.

Amends 1f6bd8bfb2.

Task-number: QTBUG-66447
Change-Id: Iae889ea416b633c9307da9535dfb51ad1dbf288e
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/plugins/platforms/windows/qwindowsdrag.cpp

@@ -412,7 +412,8 @@ QWindowsOleDropSource::QueryContinueDrag(BOOL fEscapePressed, DWORD grfKeyState)
                     const QPoint localPos = m_windowUnderMouse->handle()->mapFromGlobal(globalPos);
                     QWindowSystemInterface::handleMouseEvent(m_windowUnderMouse.data(),
                                                              QPointF(localPos), QPointF(globalPos),
-                                                             QWindowsMouseHandler::queryMouseButtons());
+                                                             QWindowsMouseHandler::queryMouseButtons(),
+                                                             Qt::LeftButton, QEvent::MouseButtonRelease);
                 }
             }
             m_currentButtons = Qt::NoButton;