Fix find scope expanding

We now use two cursors, with the first one being positioned at the
character before the find scope starts. This makes it possible
to extend the scope when typing at the beginning or the end of
it. This is more what the user expects. The effect is noticable
with find&replace of words at the beginning or end of the scope.

src/plugins/texteditor/basetexteditor.h

@@ -461,7 +461,7 @@ private slots:
     void memorizeCursorPosition();
     void restoreCursorPosition();
     void highlightSearchResults(const QString &txt, Find::IFindSupport::FindFlags findFlags);
-    void setFindScope(const QTextCursor &, int);
+    void setFindScope(const QTextCursor &start, const QTextCursor &end, int);
     void currentEditorChanged(Core::IEditor *editor);
     void maybeEmitContentsChangedBecauseOfUndo();