Fix MainWindow not propagating close events to docked widgets

Nested FloatingWindows already supported it, so make it consistent.

Personal take: In a non-docking world, users can override their
main window close event and prevent a close, to save a document
or such. However, in a docking world, the main window developer
won't know which widgets are docked, so forwarding needs to happen,
as some might have documents to save.

src/MainWindow.cpp

@@ -156,3 +156,8 @@ QRect MainWindow::centralAreaGeometry() const
 {
     return centralWidget()->geometry();
 }
+
+void MainWindow::closeEvent(QCloseEvent *ev)
+{
+    onCloseEvent(ev);
+}

src/MainWindow.h

@@ -57,6 +57,7 @@ public:
     void setCenterWidgetMargins(const QMargins &margins);
 
 protected:
+    void closeEvent(QCloseEvent *) override;
     void resizeEvent(QResizeEvent *) override;
     QRect centralAreaGeometry() const override;
 

src/MainWindowBase.cpp

@@ -39,6 +39,8 @@
 # include "DockWidget.h"
 #endif
 
+#include <QCloseEvent>
+
 using namespace KDDockWidgets;
 
 static LayoutWidget *createLayoutWidget(MainWindowBase *mainWindow, MainWindowOptions options)
@@ -791,3 +793,8 @@ QWidgetOrQuick *MainWindowBase::persistentCentralWidget() const
 
     return nullptr;
 }
+
+void MainWindowBase::onCloseEvent(QCloseEvent *e)
+{
+    d->m_layoutWidget->onCloseEvent(e);
+}

src/MainWindowBase.h

@@ -223,6 +223,7 @@ public:
     QRect windowGeometry() const;
 
 protected:
+    void onCloseEvent(QCloseEvent *);
     void setUniqueName(const QString &uniqueName);
     void onResized(QResizeEvent *); // Because QtQuick doesn't have resizeEvent()
     virtual QMargins centerWidgetMargins() const = 0;