How to make visual effect blur in SwiftUI for macOS

Issue #724

We can use .blur modifier, but with VisualEffectView gives us more options for material and blending mode.

public struct VisualEffectView: NSViewRepresentable {
    let material: NSVisualEffectView.Material
    let blendingMode: NSVisualEffectView.BlendingMode

    public init(
        material: NSVisualEffectView.Material = .contentBackground,
        blendingMode: NSVisualEffectView.BlendingMode = .withinWindow
    ) {
        self.material = material
        self.blendingMode = blendingMode
    }

    public func makeNSView(context: Context) -> NSVisualEffectView {
        let visualEffectView = NSVisualEffectView()
        visualEffectView.material = material
        visualEffectView.blendingMode = blendingMode
        visualEffectView.state = NSVisualEffectView.State.active
        return visualEffectView
    }

    public func updateNSView(_ visualEffectView: NSVisualEffectView, context: Context) {
        visualEffectView.material = material
        visualEffectView.blendingMode = blendingMode
    }
}