Fix initial position of controls with layout insets in wxOSX.

For such controls (e.g. wxButton, wxChoice, wxGauge), their initial position
was different from the one specified when creating them, even though calling
SetPosition() later did position them at exactly the position passed as
argument.

See #16780.

src/osx/window_osx.cpp

@@ -456,9 +456,16 @@ void wxWindowMac::MacChildAdded()
 #endif
 }
 
-void wxWindowMac::MacPostControlCreate(const wxPoint& WXUNUSED(pos),
+void wxWindowMac::MacPostControlCreate(const wxPoint& pos,
                                        const wxSize& WXUNUSED(size))
 {
+    // Some controls may have a nonzero layout inset,
+    // so we may need to adjust control position.
+    if ( pos.IsFullySpecified() && GetPosition() != pos )
+    {
+        SetPosition(pos);
+    }
+
     // todo remove if refactoring works correctly
 #if 0
     wxASSERT_MSG( GetPeer() != NULL && GetPeer()->IsOk() , wxT("No valid mac control") ) ;