Spanner: migrate streaming methods to gapic#3139

yihanzhen merged 3 commits into

googleapis:spanner-gapic-migrationgoogleapis/google-cloud-java:spanner-gapic-migrationfrom

yihanzhen:spanner-gapic-migration-streamingyihanzhen/google-cloud-java:spanner-gapic-migration-streamingCopy head branch name to clipboard