[SPARK-40142][PYTHON][SQL][FOLLOW-UP] Make pyspark.sql.functions examples self-contained (FINAL)

[khalidmammadov]

What changes were proposed in this pull request?

It's part of the Pyspark docstrings improvement series (#37592, #37662, #37686, #37786, #37797, #37850)

In this PR I mainly covered missing parts in the docstrings adding some more examples where it needed.

I have also made all examples self explanatory by providing DataFrame creation command where it was missing for clarity to a user.

This should complete "my take" on functions.py docstrings & example improvements.

Why are the changes needed?

To improve PySpark documentation

Does this PR introduce any user-facing change?

Yes, documentation

How was this patch tested?

PYTHON_EXECUTABLE=python3.9 ./dev/lint-python
./python/run-tests --testnames pyspark.sql.functions
bundle exec jekyll build

[AmplabJenkins]

Can one of the admins verify this patch?

[khalidmammadov]

@srowen @itholic @HyukjinKwon Please review

[HyukjinKwon]

Thanks for finishing this work, @khalidmammadov.

[khalidmammadov]

Thanks for finishing this work, @khalidmammadov.

Happy to help

[srowen]

Merged to master

[itholic]

Thanks for your efforts to finish this work!