Fix crash when using wxNotebook with glib 2.73 or later

Make GTK notebook log suppression opt-in to avoid a fatal error when the
application calls g_log_set_writer_func() itself, as doing it more than
once immediately kills the application with glib 2.73 and there is no
way to check if it had been already done or not (you have to admire the
purity of the API design here).

This is unfortunate as 99% of the wxWidgets applications that do _not_
call g_log_set_writer_func() would now show the spurious diagnostics by
default again, but preferable to making the remaining 1% crash, and
there doesn't seem to be any other solution.

Call the new GTKAllowDiagnosticsControl() function in the notebook
sample to at least still avoid getting the spurious diagnostic messages
described in #22176 there.

See #22717,.

interface/wx/app.h

@@ -1061,6 +1061,25 @@ public:
     */
     static void GTKSuppressDiagnostics(int flags = -1);
 
+    /**
+        Allows wxWidgets to selectively suppress some GTK messages.
+
+        This function can be called to allow wxWidgets to control GTK message
+        logging. You must @e not call it if your application calls the @c
+        g_log_set_writer_func() function itself, as this function can be only
+        called once.
+
+        It is recommended to call this function in your overridden version of
+        wxApp::OnInit() to allow wxWidgets to suppress some spurious GTK error
+        messages, e.g. the ones that happen whenever wxNotebook pages are
+        removed with the current GTK versions.
+
+        @onlyfor{wxgtk}
+
+        @since 3.2.1
+     */
+    static void GTKAllowDiagnosticsControl();
+
     ///@}
 
     /**

interface/wx/notebook.h

@@ -145,6 +145,10 @@ public:
 
     /**
         Destroys the wxNotebook object.
+
+        @note When using wxGTK, destroying notebook can result in spurious GTK
+        diagnostic messages, you may use wxApp::GTKAllowDiagnosticsControl() to
+        suppress them.
     */
     virtual ~wxNotebook();