[TIMOB-25253] Windows: backgroundGradient should have a default startPoint and endPoint

Description

Defining a backgroundGradient without a startPoint or endPoint should default to a value Docs: https://github.com/appcelerator/titanium_mobile/blob/6f50122643f87a89523bf27af3186f597a9a55df/apidoc/Titanium/UI/View.yml#L1788 Android: https://github.com/appcelerator/titanium_mobile/blob/a8aceeaeee02ed9c8ea70c835a0e78960e254a55/android/titanium/src/java/org/appcelerator/titanium/view/TiGradientDrawable.java#L29 iOS (I think): https://github.com/appcelerator/titanium_mobile/blob/8ab7ac87ef1663c4cd8b50afc59b3bea72f31d53/iphone/Classes/TiGradient.m#L210-L215 Note that on Android the value stated in the docs doesn't give them same outcome as the default value, below is what obtains the default on Android It does work as expected on Windows

var _window = Ti.UI.createWindow();
var buttonAddFav = Titanium.UI.createButton({
    title: 'add2favs',
    backgroundGradient:  {
        type: 'linear',
        startPoint: {x: 0.0, y: 0.0},
        endPoint: {x: 0.0, y: "100%"},
        colors: [{ color: '#aaa', offset: 0.0 }, { color: '#f00', offset: 0.25 }]
    }
});
_window.add(buttonAddFav);
_window.open()

Steps to reproduce

Add the above to an app.js and build for Windows

Comment out startPoint and endPoint

Actual

After commenting the values out the gradient disappears

Expected

The gradient should stay the same after commenting the values out