[NUI] Fix FlexLayout OnMeasure to calculate size correctly

[NUI] Fix FlexLayout OnMeasure to calculate size correctly

Previously, the measured size of FlexLayout with WrapContent could be
calculated like MatchParent.
The above issue happened in the following case.
Tizen.NUI.Components.DialogPage.ShowAlertDialog("Title", "Message", null);

To resolve the above issue without breaking backward compatibility,
FlexLayout OnMeasure has been fixed to use ResolveSizeAndState()
instead of GetDefaultSize() when calculating the measured size.

To test the issue, showing a dialog without action button case has
been added to Tizen.NUI.StyleGuide.