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

include/wx/dialog.h

@@ -133,9 +133,16 @@ public:
     // platforms which have hardware buttons replacing OK/Cancel and such)
     wxSizer *CreateButtonSizer(long flags);
 
+    // returns a sizer containing the given one and a static line separating it
+    // from the preceding elements if it's appropriate for the current platform
+    wxSizer *CreateSeparatedSizer(wxSizer *sizer);
+
     // returns the sizer containing CreateButtonSizer() below a separating
     // static line for the platforms which use static lines for items
     // separation (i.e. not Mac)
+    //
+    // this is just a combination of CreateButtonSizer() and
+    // CreateSeparatedSizer()
     wxSizer *CreateSeparatedButtonSizer(long flags);
 
 #if wxUSE_BUTTON