Vendor dependencies

Let's see how I like this workflow.

vendor/wasm-bindgen/tests/headless/strings.js

@@ -0,0 +1,21 @@
+export function test_string_roundtrip(f) {
+  const test = expected => {
+    const actual = f(expected);
+    if (actual === expected)
+      return;
+    throw new Error(`string roundtrip "${actual}" != "${expected}"`);
+  };
+
+  test('');
+  test('a');
+  test('💖');
+
+  test('a longer string');
+  test('a longer 💖 string');
+
+  test('\uFEFFbar');
+}
+
+export function identity(s) {
+  return s;
+}