Add primaryBackgroundStyle option to splitView

[frane]

This PR adds the primaryBackgroundStyle option in splitView to enable translucent sidebars when developing Mac Catalyst apps. Like splitView it's iOS only and requires iOS 13+, the moment it seems to only have an effect on Mac apps and not affect apps running on iOS, see: https://developer.apple.com/documentation/uikit/uisplitviewcontroller/3238075-primarybackgroundstyle

The following layout

Navigation.events().registerAppLaunchedListener(() => {
    Navigation.setDefaultOptions({
        layout: {
            backgroundColor: 'transparent',
            componentBackgroundColor: 'transparent',
        },
        topBar: { 
            background: {translucent: true, blur: true},
            visible: false,
        }, 
    });
    Navigation.setRoot({
        root: {
            splitView: {
                master: {
                    stack: {
                        children: [
                            {
                                component: {
                                    name: 'Sidebar',
                                },
                            },
                        ],
                    },
                },
                detail: {
                    stack: {
                        children: [
                            {
                                component: {
                                    name: 'Main',
                                },
                            },
                        ],
                    },
                },
                options: {
                    displayMode: 'visible',
                    splitView: {
                       primaryBackgroundStyle: 'sidebar',
                    }
                },
            },
        },
    });
});

will produce something like this: