Extract CreateSeparatedSizer() from wxDialog::CreateSeparatedButtonSizer().

Extract the code adding a separating wxStaticLine to the sizer in its own
function to be able to reuse it in upcoming commits.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65448 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/dialog.h

@@ -248,9 +248,30 @@ public:
 
         @note Just like CreateButtonSizer(), this function may return @NULL if
               no buttons were created.
+
+        This is a combination of CreateButtonSizer() and
+        CreateSeparatedSizer().
     */
     wxSizer* CreateSeparatedButtonSizer(long flags);
 
+    /**
+        Returns the sizer containing the given one with a separating
+        wxStaticLine if necessarily.
+
+        This function is useful for creating the sizer containing footer-like
+        contents in dialog boxes. It will add a separating static line only if
+        it conforms to the current platform convention (currently it is not
+        added under Mac where the use of static lines for grouping is
+        discouraged and is added elsewhere).
+
+        @since 2.9.2
+
+        @param sizer The sizer to wrap, must be non-@NULL.
+        @return The sizer wrapping the input one or possibly the input sizer
+            itself if no wrapping is necessary.
+     */
+    wxSizer *CreateSeparatedSizer(wxSizer *sizer);
+
     /**
         Creates a wxStdDialogButtonSizer with standard buttons. @a flags is a
         bit list of the following flags: wxOK, wxCANCEL, wxYES, wxNO, wxAPPLY,