Add WebIDL support for the object type

This maps to the `Object` type in the `js_sys` crate.

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

@@ -0,0 +1,15 @@
+use wasm_bindgen::prelude::*;
+use wasm_bindgen_test::*;
+use web_sys::Performance;
+
+#[wasm_bindgen]
+extern {
+    #[wasm_bindgen(js_name = performance)]
+    static PERFORMANCE: Performance;
+}
+
+#[wasm_bindgen_test]
+fn to_json() {
+    let perf = JsValue::from(PERFORMANCE.to_json());
+    assert!(perf.is_object());
+}