[SPARK-19732][SQL][PYSPARK] Add fill functions for nulls in bool fields of datasets

## What changes were proposed in this pull request?

Allow fill/replace of NAs with booleans, both in Python and Scala

## How was this patch tested?

Unit tests, doctests

This PR is original work from me and I license this work to the Spark project

Author: Ruben Berenguel Montoro <ruben@mostlymaths.net>
Author: Ruben Berenguel <ruben@mostlymaths.net>

Closes #18164 from rberenguel/SPARK-19732-fillna-bools.