Vendor dependencies

Let's see how I like this workflow.

vendor/js-sys/tests/wasm/Object.js

@@ -0,0 +1,11 @@
+const symbol_key = Symbol();
+
+exports.map_with_symbol_key = function() {
+  return { [symbol_key]: 42 };
+};
+exports.symbol_key = function() {
+  return symbol_key;
+};
+
+exports.Foo = class {};
+exports.Bar = class {};