Add ResizableWidget

When manual resizing is enabled, the vertical widget size can be changed
by dragging the widget in the lower right corner.

lib/utils/resizable-widget.hpp

@@ -0,0 +1,34 @@
+#pragma once
+#include <QMouseEvent>
+#include <QPainter>
+#include <QWidget>
+
+namespace advss {
+
+class ResizableWidget : public QWidget {
+	Q_OBJECT
+
+public:
+	ResizableWidget(QWidget *parent = nullptr);
+
+protected:
+	void SetResizingEnabled(bool enable);
+	void mousePressEvent(QMouseEvent *event) override;
+	void mouseMoveEvent(QMouseEvent *event) override;
+	void mouseReleaseEvent(QMouseEvent *event) override;
+	void paintEvent(QPaintEvent *event) override;
+	QSize sizeHint() const override;
+	int GetCustomHeight() const { return _customHeight; }
+	void SetCustomHeight(int value) { _customHeight = value; }
+
+private:
+	bool IsInResizeArea(const QPoint &pos) const;
+
+	bool _resizingEnabled = false;
+	bool _resizing = false;
+	QPoint _lastMousePos;
+	int _customHeight = 0;
+	const int _gripSize = 15;
+};
+
+} // namespace advss