feat(protoc_plugin): use Fully-qualified service name even for Non-gRPC Service (e.g. `greet.v1.GreetService`)

The process for obtaining the service name is different Whether the grpc option is enabled.

I want to call rpc with the full service name, even when grpc is not used.
Should I add a new option?

https://github.com/google/protobuf.dart/blob/ccf104dbc36929c0f8708285d5f3a8fae206343e/protoc_plugin/lib/src/grpc_generator.dart#L36-L43

https://github.com/google/protobuf.dart/blob/ccf104dbc36929c0f8708285d5f3a8fae206343e/protoc_plugin/lib/src/client_generator.dart#L34-L39

Start by comparing protoc_plugin/lib/src/grpc_generator.dart#L36-L43 with protoc_plugin/lib/src/client_generator.dart#L34-L39 to understand how service names are obtained with and without the grpc option. Trace the generated RPC call path and determine how the requested fully-qualified name should be specified; done means non-gRPC services use names such as greet.v1.GreetService without changing gRPC behavior.

Written by the indexing model from the issue text.