Vendor dependencies

Let's see how I like this workflow.

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

@@ -0,0 +1,16 @@
+use wasm_bindgen::prelude::*;
+use wasm_bindgen_test::*;
+
+#[wasm_bindgen(module = "/tests/headless/strings.js")]
+extern "C" {
+    fn test_string_roundtrip(c: &Closure<dyn Fn(String) -> String>);
+
+    fn identity(s: &str) -> String;
+}
+
+#[wasm_bindgen_test]
+fn string_roundtrip() {
+    test_string_roundtrip(&Closure::wrap(Box::new(|s| s)));
+
+    assert_eq!("\u{feff}bar", &identity("\u{feff}bar"));
+}