SwiftUI GeometryReader 的布局不在屏幕中间

解决办法：

var body: some View {
    GeometryReader { geometry in
        ImageContent()
        .position(x: geometry.frame(in: .local).midX, y: geometry.frame(in: .local).midY)
    }
}

参考：SwiftUI GeometryReader does not layout custom subviews in center