usb: unify ControlHandler+DeviceStateHandler, route all control requests to all handlers.

- Allows classes to handle vendor requests.
- Allows classes to use a single handler for multiple interfaces.
- Allows classes to access the other events (previously only `reset` was available).

examples/rp/src/bin/usb_ethernet.rs

@@ -73,7 +73,6 @@ async fn main(spawner: Spawner) {
         &mut singleton!([0; 256])[..],
         &mut singleton!([0; 256])[..],
         &mut singleton!([0; 128])[..],
-        None,
     );
 
     // Our MAC addr.

examples/rp/src/bin/usb_serial.rs

@@ -53,7 +53,6 @@ async fn main(_spawner: Spawner) {
         &mut config_descriptor,
         &mut bos_descriptor,
         &mut control_buf,
-        None,
     );
 
     // Create classes on the builder.