feat(tonic): add Interceptor trait (#713)

* Expose `Interceptor` trait.

* Revert changes to public API surface.

* Rename types, add deprecated alias for old names.

examples/src/tower/client.rs

@@ -15,7 +15,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     let channel = ServiceBuilder::new()
         // Interceptors can be also be applied as middleware
-        .layer(tonic::service::interceptor_fn(intercept))
+        .layer(tonic::service::interceptor(intercept))
         .layer_fn(AuthSvc::new)
         .service(channel);
 

examples/src/tower/server.rs

@@ -47,7 +47,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         // Apply our own middleware
         .layer(MyMiddlewareLayer::default())
         // Interceptors can be also be applied as middleware
-        .layer(tonic::service::interceptor_fn(intercept))
+        .layer(tonic::service::interceptor(intercept))
         .into_inner();
 
     Server::builder()