Simplify type for actix_web::App?

I'm trying to write a function that builds my app, that way it can be reused between my `main` function and my tests. Unfortunate, the type parameters for `actix_web::App` or the `IntoServiceFactory` traits are incredibly verbose. Ideally doing something like this would be straightforward:

```rust
fn create_app() -> actix_web::App {
let templates = tera::Tera::new("templates/*").unwrap();
actix_web::App::new()
.data(AppState { templates })
.route("/", actix_web::web::get().to(index))
.route("/tool/", actix_web::web::post().to(tool))
}
```

I think the right solution might be a type alias that would let you do `-> impl Something`, but I'm open to suggestions on what the right way to handle this ergonomic issue are.

Compare the desired `fn create_app() -> actix_web::App` shape with the current `actix_web::App` and `IntoServiceFactory` APIs, using the issue's shared builder example as the starting point. Done means an agreed ergonomic approach lets the app builder be reused between `main` and tests without requiring verbose type parameters, while preserving the shown routes.

Rédigé par le modèle d'indexation à partir du texte de l'issue.