Missing proto `fieldmaskpb` package (for known types)

[inliquid]

When some message contains field of google.protobuf.FieldMask type, protoc-gen-go-plugin generates code with this import:

fieldmaskpb "github.com/knqyf263/go-plugin/types/known/fieldmaskpb"

However this package is not present in go-plugin repo.

This makes it not possible to use google.protobuf.FieldMask.