(fix): Generics on Enums

[cmuramoto]

Consider the following proto file:

syntax = "proto3";

package foo;

option java_multiple_files = true;

enum CurrencyType {
    USD = 0;
    BRL = 1;
}

message Value {
    uint32 decimal = 1;
    uint32 cents = 2;
    CurrencyType type = 3;
}

The generated enum implements ProtoEnum with no type, but its associated converter is typed:

public enum CurrencyType implements ProtoEnum {
...
  enum CurrencyTypeConverter implements ProtoEnum.EnumConverter<CurrencyType> {
    INSTANCE;
  }

}

This leads to compiler issues at JsonSource::readEnum call sites. Excerpt for mergeFrom

 case 3575610: {
          if (input.isAtField(FieldNames.type)) {
            if (!input.trySkipNullValue()) {
              final ProtoEnum value = input.readEnum(CurrencyType.converter()); // compiler error on eclipse
              if (value != null) {
                type = value.getNumber();
                bitField0_ |= 0x00000004;
              } else {
                input.skipUnknownEnumValue();
              }
            }
          } else {
            input.skipUnknownField();
          }
          break;
        }

Either the converter should be implemented as a raw type or enum should not implement ProtoMessage as a raw type.

[ennerf]

That was an oversight. Thanks.

[ennerf]

I just did a 1.1.1 release that among other things includes this PR and the collisions you mentioned before