Allow automatic OS-provided tabbing to be disabled in wxOSX

macOS 10.12+ implements automatic tabbing in the OS. This adds
entries to the menus and also adds a tab bar. Some applications
might want to disable this, so provide an interface for doing this.

Closes https://github.com/wxWidgets/wxWidgets/pull/1674

interface/wx/app.h

@@ -1068,6 +1068,21 @@ public:
     */
     virtual bool OSXIsGUIApplication();
 
+    /**
+        Enable the automatic tabbing features of macOS.
+
+        This feature is native to the operating system. When it is enabled, macOS
+        will automatically place windows inside tabs and show a tab bar in the
+        application. Entries are also added to the View menu to show/hide the tab bar.
+
+        @onlyfor{wxosx}
+
+        @remarks Requires macOS 10.12+, does nothing under earlier OS versions.
+
+        @since 3.1.4
+    */
+    bool OSXEnableAutomaticTabbing(bool enable);
+
     //@}
 
 };