Implement WasmBindgen executor and reorganize

src/element.rs

@@ -0,0 +1,9 @@
+/// A generic widget.
+///
+/// This is an alias of an `iced_native` element with a default `Renderer`.
+#[cfg(not(target_arch = "wasm32"))]
+pub type Element<'a, Message> =
+    iced_winit::Element<'a, Message, iced_wgpu::Renderer>;
+
+#[cfg(target_arch = "wasm32")]
+pub use iced_web::Element;