Fix Handler::with_state not working if request body was changed via layer (#1536)

Previously

```rust
handler.layer(RequestBodyLimitLayer::new(...)).with_state(...)
```

didn't work because we required the same request body all the way
through.

examples/key-value-store/Cargo.toml

@@ -15,5 +15,6 @@ tower-http = { version = "0.3.0", features = [
     "limit",
     "trace",
 ] }
+tower-layer = "0.3.2"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }