Invalid UTF-8 in strings are not rejected

[kirk91]

The proto2 and proto3 specifications state that the string type must be encoded as valid UTF-8, and the golang protobuf implementation would reject invalid utf8 string on marshaling and unmarshaling in proto3.

I am wondering if vtprotobuf can support UTF-8 string validation for proto3 to ensure consistent behavior with the canonical implementation.

Here are the related issues and changes:

• Invalid UTF-8 in strings are not rejected golang/protobuf#484
• proto: reject invalid UTF-8 in strings golang/protobuf#499
• proto: revert proto2 string UTF-8 validation golang/protobuf#622
• proto: revert UTF-8 validation for proto2 golang/protobuf#628