Vendor dependencies

Let's see how I like this workflow.

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

@@ -0,0 +1,11 @@
+exports.proxy_target = function() {
+  return { a: 100 };
+};
+
+exports.proxy_handler = function() {
+  return {
+    get: function(obj, prop) {
+      return prop in obj ? obj[prop] : 37;
+    }
+  };
+};