feat(swarm): Add wasm-bindgen executor (#3115)

swarm/src/executor.rs

@@ -59,3 +59,14 @@ impl Executor for AsyncStdExecutor {
         let _ = async_std::task::spawn(future);
     }
 }
+
+#[cfg(feature = "wasm-bindgen")]
+#[derive(Default, Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
+pub struct WasmBindgenExecutor;
+
+#[cfg(feature = "wasm-bindgen")]
+impl Executor for WasmBindgenExecutor {
+    fn exec(&self, future: Pin<Box<dyn Future<Output = ()> + Send>>) {
+        wasm_bindgen_futures::spawn_local(future)
+    }
+}