add basic support to show refactor markers

See BaseTextEditor::setRefactorMarkers(...). The markers support
a clicked signal via BaseTextEditor and tooltips. They feature
a cursor, but are always positioned at the end of the line (not block!).

As special gimmick they do extend the document width when they
are positioned outside the document area.

src/plugins/texteditor/refactoroverlay.h

@@ -0,0 +1,51 @@
+#ifndef REFACTOROVERLAY_H
+#define REFACTOROVERLAY_H
+
+#include "basetexteditor.h"
+#include <QTextCursor>
+#include <QObject>
+#include <QIcon>
+
+namespace TextEditor {
+namespace Internal {
+
+struct  TEXTEDITOR_EXPORT RefactorMarker {
+    inline bool isValid() const { return !cursor.isNull(); }
+    QTextCursor cursor;
+    QString tooltip;
+    QIcon icon;
+    mutable QRect rect; // used to cache last drawing positin in document coordinates
+    QVariant data;
+};
+
+typedef QList<RefactorMarker> RefactorMarkers;
+
+class  TEXTEDITOR_EXPORT RefactorOverlay : public QObject
+{
+    Q_OBJECT
+public:
+    explicit RefactorOverlay(BaseTextEditor *editor);
+
+    bool isEmpty() const { return m_markers.isEmpty(); }
+    void paint(QPainter *painter, const QRect &clip);
+
+    void setMarkers(const RefactorMarkers &markers) { m_markers = markers; }
+    RefactorMarkers markers() const { return m_markers; }
+
+    void clear() { m_markers.clear(); }
+
+    RefactorMarker markerAt(const QPoint &pos) const;
+
+private:
+    void paintMarker(const RefactorMarker& marker, int position, QPainter *painter, const QRect &clip);
+    RefactorMarkers m_markers;
+    BaseTextEditor *m_editor;
+    int m_maxWidth;
+    QIcon m_icon;
+
+};
+
+}
+}
+
+#endif // REFACTOROVERLAY_H