Added further API for intercepting deletion and content insertion

Added simple implementation of locked objects to sample


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70465 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/richtext/richtextbuffer.h

@@ -3231,6 +3231,12 @@ public:
 
     virtual wxRichTextObject* Clone() const { return new wxRichTextParagraphLayoutBox(*this); }
 
+    /**
+        Prepares the content just before insertion (or after buffer reset).
+        Currently is only called if undo mode is on.
+    */
+    virtual void PrepareContent(wxRichTextParagraphLayoutBox& container);
+
     /**
         Insert fragment into this box at the given position. If partialParagraph is true,
         it is assumed that the last (or only) paragraph is just a piece of data with no paragraph