Vendor dependencies

Let's see how I like this workflow.

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

@@ -0,0 +1,7 @@
+// Used for `Array.rs` tests
+exports.populate_array = function(arr, start, len) {
+  var isBigInt = typeof(arr[0]) === "bigint";
+  for (i = 0; i < len; i++) {
+    arr[i] = isBigInt ? BigInt(start + i) : start + i;
+  }
+};