Impl std::istream variant to Load and LoadOrDie
Impl std::istream variant to Load and LoadOrDie

Implemented for SentencePieceProcessor:
bool SentencePieceProcessor::Load(std::istream &istream)
void SentencePieceProcessor::LoadOrDie(std::istream &istream)
google/sentencepiece,google/sentencepiece,tsuchm/sentencepiece,google/sentencepiece,google/sentencepiece,tsuchm/sentencepiece,tsuchm/sentencepiece,tsuchm/sentencepiece