Handle [Unforgeable] on interfaces

In addition to handling it on methods look like it also shows up on interfaces!

Closes #780

crates/web-sys/tests/wasm/location.rs

@@ -0,0 +1,56 @@
+use wasm_bindgen_test::*;
+use web_sys::Window;
+
+#[wasm_bindgen_test]
+fn href() {
+    let loc = Window::location();
+    loc.href().unwrap();
+}
+
+#[wasm_bindgen_test]
+fn origin() {
+    let loc = Window::location();
+    loc.origin().unwrap();
+}
+
+#[wasm_bindgen_test]
+fn protocol() {
+    let loc = Window::location();
+    loc.protocol().unwrap();
+}
+
+#[wasm_bindgen_test]
+fn host() {
+    let loc = Window::location();
+    loc.host().unwrap();
+}
+
+#[wasm_bindgen_test]
+fn hostname() {
+    let loc = Window::location();
+    loc.hostname().unwrap();
+}
+
+#[wasm_bindgen_test]
+fn port() {
+    let loc = Window::location();
+    loc.port().unwrap();
+}
+
+#[wasm_bindgen_test]
+fn pathname() {
+    let loc = Window::location();
+    loc.pathname().unwrap();
+}
+
+#[wasm_bindgen_test]
+fn search() {
+    let loc = Window::location();
+    loc.search().unwrap();
+}
+
+#[wasm_bindgen_test]
+fn hash() {
+    let loc = Window::location();
+    loc.hash().unwrap();
+}