[TIMOB-11941] iOS: When showing a view, we should first relayout

*Problem description* If you run the testcase, when pushing the button, the red view will appear and you will see it of width 50 before going quickly to 200. Actually you expect it to be directly 200 when you show it as you set the property before calling "show." So the view should force itself to relayout before becoming visible. It comes from the method willShow of TiViewProxy. *Pull request* See comment. *Test case*

var win = Ti.UI.createWindow({backgroundColor:'white'});

var label = Ti.UI.createLabel({
    height:50,
    width:50,
    top:2,
    backgroundColor:'red',
    visible:false
});

win.add(label);

var b1 = Ti.UI.createButton({
    title:'ADD CHILD',
    bottom:10,
    height:35
});

b1.addEventListener('click',function(){
	label.width = 200;
    label.show();
});

win.add(b1);
win.open();