protobuf well known types generated incorrectly

protoc should generate extra helper methods for well known types, such as Timesamp.toDate.
However these don't get generated when you use the library option to protoc, and it appears that rules_closure always uses the library option.

Start by reproducing the well-known-type generation through protoc with the library option used by rules_closure, and compare it with generation without that option. Check whether the expected Timestamp.toDate helper appears; done means rules_closure produces the extra helper methods for well-known types.

Written by the indexing model from the issue text.