iPhone X/XS/XR/XS Max 的屏幕适配

鉴于iPhone X/XS/XR/XS Max底部都会有安全距离，所以可以利用safeAreaInsets.bottom > 0.0来判断是否是iPhone X/XS/XR/XS Max。

safeAreaInsets支持iOS11及以后。

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