Support State with #[derive(FromRequest[Parts])] (#1391)

* Support `State` with `#[derive(FromRequest[Parts])]`

Fixes https://github.com/tokio-rs/axum/issues/1314

This makes it possible to extract things via `State` in
`#[derive(FromRequet)]`:

```rust
struct Foo {
    state: State<AppState>,
}
```

The state can also be inferred in a lot of cases so you only need to
write:

```rust
struct Foo {
    // since we're using `State<AppState>` we know the state has to be
    // `AppState`
    state: State<AppState>,
}
```

Same for

```rust
struct Foo {
    #[from_request(via(State))]
    state: AppState,
}
```

And

```rust
struct AppState {}
```

I think I've covered all the edge cases but there are (unsurprisingly) a
few.

* make sure things can be combined with other extractors

* main functions in ui tests don't need to be async

* Add test for multiple identicaly state types

* Add failing test for multiple states

axum-macros/tests/from_request/fail/state_infer_multiple_different_types.rs

@@ -0,0 +1,22 @@
+use axum_macros::FromRequest;
+use axum::extract::State;
+
+#[derive(FromRequest)]
+struct Extractor {
+    inner_state: State<AppState>,
+    other_state: State<OtherState>,
+}
+
+#[derive(Clone)]
+struct AppState {}
+
+#[derive(Clone)]
+struct OtherState {}
+
+fn assert_from_request()
+where
+    Extractor: axum::extract::FromRequest<AppState, axum::body::Body, Rejection = axum::response::Response>,
+{
+}
+
+fn main() {}

axum-macros/tests/from_request/fail/state_infer_multiple_different_types.stderr

@@ -0,0 +1,23 @@
+error[E0277]: the trait bound `AppState: FromRef<S>` is not satisfied
+ --> tests/from_request/fail/state_infer_multiple_different_types.rs:6:18
+  |
+6 |     inner_state: State<AppState>,
+  |                  ^^^^^ the trait `FromRef<S>` is not implemented for `AppState`
+  |
+  = note: required because of the requirements on the impl of `FromRequestParts<S>` for `State<AppState>`
+help: consider extending the `where` clause, but there might be an alternative better way to express this requirement
+  |
+4 | #[derive(FromRequest, AppState: FromRef<S>)]
+  |                     ++++++++++++++++++++++
+
+error[E0277]: the trait bound `OtherState: FromRef<S>` is not satisfied
+ --> tests/from_request/fail/state_infer_multiple_different_types.rs:7:18
+  |
+7 |     other_state: State<OtherState>,
+  |                  ^^^^^ the trait `FromRef<S>` is not implemented for `OtherState`
+  |
+  = note: required because of the requirements on the impl of `FromRequestParts<S>` for `State<OtherState>`
+help: consider extending the `where` clause, but there might be an alternative better way to express this requirement
+  |
+4 | #[derive(FromRequest, OtherState: FromRef<S>)]
+  |                     ++++++++++++++++++++++++

axum-macros/tests/from_request/fail/unknown_attr_container.stderr

@@ -1,4 +1,4 @@
-error: expected `via` or `rejection`
+error: expected one of: `via`, `rejection`, `state`
  --> tests/from_request/fail/unknown_attr_container.rs:4:16
   |
 4 | #[from_request(foo)]