Correctly handle padding in JS2

feature_tests/js/test/struct.mjs

@@ -1,5 +1,5 @@
 import test from 'ava';
-import { MyEnum, MyStruct } from "diplomat-wasm-js-feature-tests";
+import { MyEnum, MyStruct, ScalarPairWithPadding, BigStructWithStuff } from "diplomat-wasm-js-feature-tests";
 
 test("Verify invariants of struct", t => {
     const s = MyStruct.new_("hello");
@@ -16,4 +16,16 @@ test("Verify invariants of struct", t => {
 test("Test struct creation", t => {
     const s = new MyStruct(17, true, 209, 1234n, 5991, '餐'.codePointAt(0), MyEnum.B);
     t.is(s.intoA(), 17);
-});
+});
+
+test("Test struct layout: scalar pair layout", t => {
+    const s = new ScalarPairWithPadding(122, 414);
+    s.assertValue();
+    t.is(true, true); // Ava doesn't like tests without assertions
+});
+
+test("Test struct layout: complex struct with multiple padding types and contained scalar pair", t => {
+    const s = new BigStructWithStuff(101, 505, 9345, new ScalarPairWithPadding(122, 414), 99);
+    s.assertValue(853);
+    t.is(true, true); // Ava doesn't like tests without assertions
+});