Moved the multisplitter wrapper outside of multisplitter/

As it depends on kddw framework, while multisplitter/ is the
agnostic layouting engine

src/private/widgets/MultiSplitter.cpp

@@ -0,0 +1,100 @@
+/*
+  This file is part of KDDockWidgets.
+
+  Copyright (C) 2018-2020 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 widget that supports an arbitrary number of splitters (called Separators) in any
+ * combination of vertical/horizontal.
+ *
+ * @author Sérgio Martins \<sergio.martins@kdab.com\>
+ */
+
+
+#include "MultiSplitter_p.h"
+#include "MultiSplitterLayout_p.h"
+#include "../Logging_p.h" // TODO
+#include "MainWindowBase.h"
+#include "FloatingWindow_p.h"
+#include "LayoutSaver.h"
+
+#include <QScopedValueRollback>
+
+using namespace KDDockWidgets;
+
+MultiSplitter::MultiSplitter(QWidgetOrQuick *parent)
+    : QWidgetAdapter(parent)
+    , m_layout(new MultiSplitterLayout(this))
+{
+    connect(m_layout, &MultiSplitterLayout::minimumSizeChanged, this, [this] (QSize sz) {
+        setMinimumSize(sz);
+    });
+
+    connect(m_layout, &MultiSplitterLayout::sizeChanged, this, [this] (QSize sz) {
+        if (!m_inResizeEvent && !LayoutSaver::restoreInProgress())
+            resize(sz);
+    });
+
+    setMinimumSize(m_layout->minimumSize());
+}
+
+MultiSplitter::~MultiSplitter()
+{
+}
+
+void MultiSplitter::onLayoutRequest()
+{
+    m_layout->updateSizeConstraints();
+}
+
+bool MultiSplitter::onResize(QSize newSize)
+{
+    qCDebug(sizing) << Q_FUNC_INFO << "; new=" << newSize
+                    << "; window=" << window();
+
+    QScopedValueRollback<bool>(m_inResizeEvent, true); // to avoid re-entrancy
+
+    if (!LayoutSaver::restoreInProgress()) {
+        // don't resize anything while we're restoring the layout
+        m_layout->setSize(newSize);
+    }
+
+    return false; // So QWidget::resizeEvent is called
+}
+
+bool MultiSplitter::isInMainWindow() const
+{
+    return mainWindow() != nullptr;
+}
+
+MainWindowBase *MultiSplitter::mainWindow() const
+{
+    if (auto pw = parentWidget()) {
+        // Note that if pw is a FloatingWindow then pw->parentWidget() can be a MainWindow too, as it's parented
+        if (pw->objectName() == QLatin1String("MyCentralWidget"))
+            return qobject_cast<MainWindowBase*>(pw->parentWidget());
+    }
+
+    return nullptr;
+}
+
+FloatingWindow *MultiSplitter::floatingWindow() const
+{
+    return qobject_cast<FloatingWindow*>(parentWidget());
+}