Fix RPC name conflicts with generated code

[lucia3e8]

Motivation

Issues: #747 and #1253

Still a draft - need to add tests

TLDR: Tonic adds predefined methods to codegenned structs, like connect. If that name conflicts with an RPC name, the resulting code fails to compile.

Solution

This is a problem for other gRPC codegenners too. The C++ one just prepends the problematic method names with a _.
I took the same approach here.

For example, given the RPC definition

syntax = "proto3";
service MyService {
  rpc Connect(ConnectRequest) returns (ConnectResponse);
}

Will generate the following code now

    impl MyServiceClient<tonic::transport::Channel> {
        /// VVVVVVV This is the tonic-provided method
        /// Attempt to create a new client by connecting to a given endpoint.
        pub async fn connect<D>(dst: D) -> Result<Self, tonic::transport::Error>
        where
            D: std::convert::TryInto<tonic::transport::Endpoint>,
            D::Error: Into<StdError>,
        {
            let conn = tonic::transport::Endpoint::new(dst)?.connect().await?;
            Ok(Self::new(conn))
        }
    }
    impl<T> MyServiceClient<T>
    where
        T: tonic::client::GrpcService<tonic::body::BoxBody>,
        T::Error: Into<StdError>,
        T::ResponseBody: Body<Data = Bytes> + Send + 'static,
        <T::ResponseBody as Body>::Error: Into<StdError> + Send,
    {
        [...]
        /// VVVVVVV This is the method generated from the .proto file
        pub async fn _connect(
            &mut self,
            request: impl tonic::IntoRequest<super::ConnectRequest>,
        ) -> Result<tonic::Response<super::ConnectResponse>, tonic::Status> {
            [...]
        }