Add wxApp::GTKSuppressDiagnostics()

This allows to avoid GTK messages that are often more annoying and
confusing than useful.

Closes https://github.com/wxWidgets/wxWidgets/pull/2609

Closes #19347.

include/wx/gtk/app.h

@@ -58,6 +58,12 @@ public:
     // various bugs arising due to this.
     static bool GTKIsUsingGlobalMenu();
 
+    // Provide the ability to suppress GTK output. By default, all output
+    // will be suppressed, but the user can pass in a mask specifiyng the
+    // types of messages to suppress. Flags are defined by glib with the
+    // GLogLevelFlags enum.
+    static void GTKSuppressDiagnostics(int flags = -1);
+
     // implementation only from now on
     // -------------------------------