Introduce a Delete Line action that doesn't copy to clipboard

The version that does copy to clipboard is now called Cut Line, and is
still mapped to Shift+Delete by default.

src/plugins/texteditor/basetexteditor.h

@@ -370,6 +370,7 @@ public slots:
     void zoomIn(int range = 1);
     void zoomOut(int range = 1);
 
+    void cutLine();
     void deleteLine();
     void unCollapseAll();
     void collapse();
@@ -406,6 +407,9 @@ protected:
     bool canInsertFromMimeData(const QMimeData *source) const;
     void insertFromMimeData(const QMimeData *source);
 
+private:
+    void maybeSelectLine();
+
 public:
     void duplicateFrom(BaseTextEditor *editor);