Initial data commit

Task/Simple-windowed-application/Vala/simple-windowed-application.vala

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+// GTK 4
+public class Example : Gtk.Application {
+  public Example() {
+    Object(application_id: "my.application",
+      flags: ApplicationFlags.FLAGS_NONE);
+    activate.connect(() => {
+      var window = new Gtk.ApplicationWindow(this);
+      var box = new Gtk.Box(Gtk.Orientation.VERTICAL, 20);
+      var label = new Gtk.Label("There have been no clicks yet");
+      var button = new Gtk.Button.with_label("click me");
+      var clicks = 0;
+      button.clicked.connect(() => {
+        clicks++;
+        label.label = "Button clicked " + clicks.to_string() + " times";
+      });
+      box.append(label);
+      box.append(button);
+      window.set_child(box);
+      window.present();
+    });
+  }
+  public static int main(string[] argv) {
+    return new Example().run(argv);
+  }
+}