function getLaunchStoryboardContentsJSON (splashScreens, launchStoryboardImagesDir) {
    const platformLaunchStoryboardImages = mapLaunchStoryboardContents(splashScreens, launchStoryboardImagesDir);
    const contentsJSON = {
        images: [],
        info: {
            author: 'Xcode',
            version: 1
        }
    };
    contentsJSON.images = platformLaunchStoryboardImages.map(item => {
        const newItem = {
            idiom: item.idiom,
            scale: item.scale
        };

        // Xcode doesn't want any size class property if the class is "any"
        // If our size class is "com", Xcode wants "compact".
        if (item.width !== CDV_ANY_SIZE_CLASS) {
            newItem['width-class'] = IMAGESET_COMPACT_SIZE_CLASS;
        }
        if (item.height !== CDV_ANY_SIZE_CLASS) {
            newItem['height-class'] = IMAGESET_COMPACT_SIZE_CLASS;
        }

        if (item.appearence) {
            newItem.appearances = [{ appearance: 'luminosity', value: item.appearence }];
        }

        // Xcode doesn't want a filename property if there's no image for these traits
        if (item.filename) {
            newItem.filename = item.filename;
        }
        return newItem;
    });
    return contentsJSON;
}
Builds the object that represents the contents.json file for the LaunchStoryboard image set.

The resulting return looks like this:

    {
        images: [
            {
                idiom: 'universal|ipad|iphone',
                scale: '1x|2x|3x',
                width-class: undefined|'compact',
                height-class: undefined|'compact'
                ...
            }, ...
        ],
        info: {
            author: 'Xcode',
            version: 1
        }
    }

A bit of minor logic is used to map from the array of images returned from mapLaunchStoryboardContents
to the format requried by Xcode.

@param  {Array<Object>} splashScreens         splash screens as defined in config.xml for this platform
@param  {string} launchStoryboardImagesDir    project-root/Assets.xcassets/LaunchStoryboard.imageset/
@return {Object}