Move the private code into a private/ folder

It's nice to have a similar include hierarchy at build time and install
time.

It also makes things more explicit

src/private/widgets/QWidgetAdapter_widgets.cpp

@@ -0,0 +1,110 @@
+/*  This file is part of KDDockWidgets.
+
+  Copyright (C) 2019 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com
+  Author: Sérgio Martins <sergio.martins@kdab.com>
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY;
+
+
+
+  without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+/**
+ * @file
+ * @brief A class that is QWidget when building for QtWidgets, and QObject when building for QtQuick.
+ *
+ * Allows to have the same code base supporting both stacks.
+ *
+ * @author Sérgio Martins \<sergio.martins@kdab.com\>
+ */
+
+#include "QWidgetAdapter_widgets_p.h"
+#include "FloatingWindow_p.h"
+
+#include <QResizeEvent>
+#include <QMouseEvent>
+
+using namespace KDDockWidgets;
+
+QWidgetAdapter::QWidgetAdapter(QWidget *parent, Qt::WindowFlags f)
+    : QWidget(parent, f)
+{
+}
+
+QWidgetAdapter::~QWidgetAdapter()
+{
+}
+
+FloatingWindow *QWidgetAdapter::floatingWindow() const
+{
+    if (auto fw = qobject_cast<FloatingWindow*>(window()))
+        return fw;
+
+    return nullptr;
+}
+
+void QWidgetAdapter::raiseAndActivate()
+{
+    window()->raise();
+    window()->activateWindow();
+}
+
+bool QWidgetAdapter::event(QEvent *e)
+{
+    if (e->type() == QEvent::LayoutRequest)
+        onLayoutRequest();
+
+    return QWidget::event(e);
+}
+
+void QWidgetAdapter::resizeEvent(QResizeEvent *ev)
+{
+    if (!onResize(ev->size()))
+        QWidget::resizeEvent(ev);
+}
+
+void QWidgetAdapter::mousePressEvent(QMouseEvent *)
+{
+    onMousePress();
+}
+
+void QWidgetAdapter::mouseMoveEvent(QMouseEvent *ev)
+{
+    onMouseMove(ev->globalPos());
+}
+
+void QWidgetAdapter::mouseReleaseEvent(QMouseEvent *)
+{
+    onMouseRelease();
+}
+
+void QWidgetAdapter::closeEvent(QCloseEvent *e)
+{
+    onCloseEvent(e);
+}
+
+void QWidgetAdapter::setFlag(Qt::WindowType f, bool on)
+{
+    QWidget::setWindowFlag(f, on);
+}
+
+bool QWidgetAdapter::onResize(QSize) { return false; }
+void QWidgetAdapter::onLayoutRequest() {}
+
+void QWidgetAdapter::onMousePress() {}
+void QWidgetAdapter::onMouseMove(QPoint) {}
+void QWidgetAdapter::onMouseRelease() {}
+
+void QWidgetAdapter::onCloseEvent(QCloseEvent *) {}