RegisterXXXServer with grpc.ServiceRegistrar

[defool]

Is your feature request related to a problem? Please describe.
Can not register server by grpc.ServiceRegistrar, I need something like grpc/grpc-go#3966

Describe the solution you'd like

Change this line
https://github.com/golang/protobuf/blob/master/internal/gengogrpc/grpc.go#L156

to

g.P("func Register", service.GoName, "Server(s ", grpcPackage.Ident("ServiceRegistrar"), ", srv ", serverType, ") {")

Describe alternatives you've considered
None

Additional context
None

[neild]

The gRPC code generator in github.com/golang/protobuf/protoc-gen-go has been entirely superseded by google.golang.org/cmd/protoc-gen-go-grpc. We aren't making further changes to the gRPC generator in this module; it continues to exist for backwards compatibility, but users should migrate to the one in the gRPC repository at their convenience.

[neild]

Closing: gRPC changes should happen in the gRPC repository.