default Map<String, ServerMethodDefinition<?, ?>> methods() {
        return services().stream()
                         .flatMap(service -> service.getMethods().stream())
                         .distinct()
                         .collect(toImmutableMap(method -> method.getMethodDescriptor().getFullMethodName(),
                                                 Function.identity()));
    }
Returns a {@link Map} whose key is a route path and whose value is {@link ServerMethodDefinition},
which is served by this service.
grpc/src/main/java/com/linecorp/armeria/server/grpc/GrpcService.java