How to build container view in SwiftUI

Issue #780

To make a container view that accepts child content, we use ViewBuilder

struct ContainerView<Content: View>: View {
    let content: Content

    init(@ViewBuilder content: () -> Content) {
        self.content = content()
    }

    var body: some View {
        content
    }
}

From Swift 5.4, it can synthesize the init, so we can declare resultBuilder for stored property

struct AwesomeContainerView<Content: View>: View {
    @ViewBuilder
    let content: Content

    var body: some View {
        content
    }
}