[SPARK-3142][MLLIB] output shuffle data directly in Word2Vec

Sorry I didn't realize this in #2043. Ishiihara

Author: Xiangrui Meng <meng@databricks.com>

Closes #2049 from mengxr/more-w2v and squashes the following commits:

050b1c5 [Xiangrui Meng] output shuffle data directly