Generated server's service should not match full paths

## Feature Request
tonic-build 0.9.2 generates `tonic::codegen::Service` with every call matching full `URI` instead of stripping service prefix

It should strip prefix `//` and match only on method name (or better use hash)

### Crates

```
tonic-build 0.9.2
```

### Motivation

Performance

### Proposal

Generated code could be simple along lines of something like:

```
impl tonic::codegen::Service> for TaskServer
where
T: Task,
B: Body + Send + 'static,
B::Error: Into + Send + 'static,
{
type Response = http::Response;
type Error = std::convert::Infallible;
type Future = BoxFuture;
fn poll_ready(
&mut self,
_cx: &mut Context<'_>,
) -> Poll> {
Poll::Ready(Ok(()))
}
fn call(&mut self, req: http::Request) -> Self::Future {
let inner = self.inner.clone();
let path = req.uri().path();
if let Some(method) = path.strip_prefix("/tasks.Task/") {
match method {
"method1" => todo!(),
_ => todo!(),
}
}
}
}