Move axum-handle-error-extract into axum (#534)

* Move `axum-handle-error-extract` into axum

With 0.4 underway we can now nuke `axum-handle-error-extract` and move
its code directly into axum.

So this replaces the old `HandleErrorLayer` with one that supports async
functions and extractors.

* changelog

* fix CI

examples/print-request-response/src/main.rs

@@ -29,7 +29,7 @@ async fn main() {
         .route("/", post(|| async move { "Hello from `POST /`" }))
         .layer(
             ServiceBuilder::new()
-                .layer(HandleErrorLayer::new(|error| {
+                .layer(HandleErrorLayer::new(|error| async move {
                     (
                         StatusCode::INTERNAL_SERVER_ERROR,
                         format!("Unhandled internal error: {}", error),