Fix Binary Conformance Test for Packe/Unpacked Repeated Fields

[TeBoring]

https://github.com/protocolbuffers/protobuf/pull/6447 https://github.com/protocolbuffers/protobuf/pull/6440

• Both packed/unpacked data should be accepted during parsing
• Without specifying, encoding should follow the default behavior (unpacked for proto2 and packed for proto3)
• When specified in field option, encoding should respect that.

[dibenede]

Need to get conformance tests running in the new repo.