Remove DockWidget::hidden() and shown() signals

Visibility isn't useful as a concept, since non current tabs
are also hidden. Instead, use DockWidget::isOpen()

src/controllers/DockWidget.cpp

@@ -879,7 +879,6 @@ void DockWidget::Private::onParentChanged()
 void DockWidget::onShown()
 {
     d->onDockWidgetShown();
-    Q_EMIT shown();
 
     d->maybeRestoreToPreviousPosition();
 
@@ -890,7 +889,6 @@ void DockWidget::onShown()
 void DockWidget::onHidden()
 {
     d->onDockWidgetHidden();
-    Q_EMIT hidden();
 }
 
 void DockWidget::onResize(QSize)

src/controllers/DockWidget.h

@@ -433,11 +433,6 @@ public:
     void onResize(QSize newSize);
 
 Q_SIGNALS:
-    ///@brief signal emitted when the DockWidget is shown. As in QEvent::Show.
-    void shown();
-
-    ///@brief signal emitted when the DockWidget is hidden. As in QEvent::Hide.
-    void hidden();
 
     ///@brief signal emitted when the icon changed
     void iconChanged();

src/qtquick/DockWidgetInstantiator.cpp

@@ -194,8 +194,6 @@ void DockWidgetInstantiator::componentComplete()
             &DockWidgetInstantiator::actualTitleBarChanged);
     connect(m_dockWidget, &Controllers::DockWidget::optionsChanged, this,
             &DockWidgetInstantiator::optionsChanged);
-    connect(m_dockWidget, &Controllers::DockWidget::shown, this, &DockWidgetInstantiator::shown);
-    connect(m_dockWidget, &Controllers::DockWidget::hidden, this, &DockWidgetInstantiator::hidden);
     connect(m_dockWidget, &Controllers::DockWidget::iconChanged, this,
             &DockWidgetInstantiator::iconChanged);
     connect(m_dockWidget, &Controllers::DockWidget::guestViewChanged, this, [this] {