Implemented python wrappers for Scala functions that don't exist in `ml.features`

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #5991 from brkyvz/ml-feat-PR and squashes the following commits:

adcca55 [Burak Yavuz] add regex tokenizer to __all__
b91cb44 [Burak Yavuz] addressed comments
bd39fd2 [Burak Yavuz] remove addition
b82bd7c [Burak Yavuz] Parity in PySpark for ml.features