feat: let pb value to native go type equals Message.filed

[yywing]

Let pb value to native go type equals Message.filed.

env: variable a is proto.Message. a.list is []string

func ReadList(v ref.Value) ref.Value {
      switch v.Value.(type) {
      case []string:
              return v
      default:
             painc("a")
      }
}

readList(a.list) will panic

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