Make wxTopLevelWindow::GetDefaultSize() public and document it.

This method is/will be needed by wxNonOwnedWindow in wxOSX but couldn't be
used as long as it was protected, so make it public. And as it seems that it
might be useful outside of wx itself, document it as well.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65260 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/toplevel.h

@@ -148,6 +148,19 @@ public:
     */
     wxWindow* GetDefaultItem() const;
 
+    /**
+        Get the default size for a new top level window.
+
+        This is used internally by wxWidgets on some platforms to determine the
+        default size for a window created using ::wxDefaultSize so it is not
+        necessary to use it when creating a wxTopLevelWindow, however it may be
+        useful if a rough estimation of the window size is needed for some
+        other reason.
+
+        @since 2.9.2
+     */
+    static wxSize GetDefaultSize();
+
     /**
         Returns the standard icon of the window. The icon will be invalid if it
         hadn't been previously set by SetIcon().