Allow updating wxBusyInfo text while it's shown

Add UpdateText() and UpdateLabel() updating the text (i.e. possibly
containing markup) or the label (just plain text) shown in the window.

Closes #14743.

Closes https://github.com/Kvaz1r/wxWidgets.git BusyInfoUpdateText14743

interface/wx/busyinfo.h

@@ -111,6 +111,23 @@ public:
     */
     wxBusyInfo(const wxString& msg, wxWindow* parent = NULL);
 
+    /**
+        Update the information text.
+
+        The @a text string may contain markup as described in
+        wxControl::SetLabelMarkup().
+
+        @since 3.1.3
+    */
+    void UpdateText(const wxString& str);
+
+    /**
+        Same as UpdateText() but doesn't interpret the string as containing markup.
+
+        @since 3.1.3
+    */
+    void UpdateLabel(const wxString& str);
+
     /**
         Hides and closes the window containing the information text.
     */