Vendor dependencies

Let's see how I like this workflow.

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

@@ -0,0 +1,19 @@
+// Used for `Function.rs` tests
+exports.get_function_to_bind = function() {
+  return function() { return this.x || 1; }
+};
+exports.get_value_to_bind_to = function() {
+  return { x: 2 };
+};
+exports.list = function() {
+  return function() {return Array.prototype.slice.call(arguments);}
+};
+exports.add_arguments = function() {
+    return function(arg1, arg2) {return arg1 + arg2}
+};
+exports.call_function = function(f) {
+  return f();
+};
+exports.call_function_arg =  function(f, arg1) {
+  return f(arg1);
+};