Add shared catalog example row and screen shim

Author: colemancda

Demo/App.swiftpm/Sources/CatalogSupport.swift

@@ -0,0 +1,31 @@
+#if canImport(AndroidSwiftUI)
+import AndroidSwiftUI
+#else
+import SwiftUI
+#endif
+
+/// Type-erased catalog screen (a small AnyView shim usable as a navigation
+/// destination while keeping the entry list homogeneous).
+struct AnyCatalogScreen: View {
+    private let content: AnyView
+    init<V: View>(_ view: V) { self.content = AnyView(view) }
+    var body: some View { content }
+}
+
+/// A titled example row shared by the playgrounds.
+struct Example<Content: View>: View {
+    let title: String
+    let content: Content
+    init(_ title: String, @ViewBuilder content: () -> Content) {
+        self.title = title
+        self.content = content()
+    }
+    var body: some View {
+        VStack(alignment: .leading, spacing: 8) {
+            Text(title)
+            content
+            Divider()
+        }
+        .padding()
+    }
+}