Add a nodejs testing function for apply_layout

This will allow making the JS test code more similar to the C++/Rust code,
allowing replacing synthetic mouse clicks.

api/sixtyfps-node/lib/index.ts

@@ -26,6 +26,16 @@ function load_native_lib() {
  */
 let native = !process.env.SIXTYFPS_NODE_NATIVE_LIB ? require('../native/index.node') : load_native_lib();
 
+/**
+ * @hidden
+ */
+interface Rect {
+    x: number,
+    y: number,
+    width: number,
+    height: number
+}
+
 /**
  * @hidden
  */
@@ -55,6 +65,10 @@ class Component {
     send_keyboard_string_sequence(s: String) {
         this.comp.send_keyboard_string_sequence(s)
     }
+
+    apply_layout(rect: Rect) {
+        this.comp.apply_layout(rect)
+    }
 }
 
 /**