feat: add slint based stuff

slint-based/ui/app-window.slint

@@ -0,0 +1,36 @@
+import { Button, VerticalBox , AboutSlint } from "std-widgets.slint";
+
+export component AppWindow inherits Window {
+    width: 320px;
+    height: 240px;
+    in-out property <int> counter: 42;
+    callback request-increase-value();
+
+    VerticalBox {
+        alignment: start;
+        Text {
+            text: "Hello World!";
+            font-size: 24px;
+            horizontal-alignment: center;
+        }
+    }
+
+    Text {
+        text: "Counter App (Slint)";
+    }
+
+    VerticalBox {
+        Text {
+            text: "Counter: \{root.counter}";
+        }
+
+        Button {
+            text: "Increase value";
+            clicked => {
+                root.request-increase-value();
+            }
+        }
+
+        // AboutSlint { }
+     }
+}