[Python] Add pyspark null functions

[mariotaddeucci]

Adding some functions to work with nulls.

I tried to add the coalesce function directly and use it on nvl and ifnull but I got the error saying the coalesce function is not a scalar function.

This PR could be converted to a draft and then adding a issue and just merge when the coalesce be added to python relational api.

[Tishj]

Thanks!
Feel free to make a PR extending our native python expression API as well when necessary.
Taking #11941 as an example shows how easy these additions can be :)

[Tishj]

Please merge with main and address the colesce todo, the linked PR has been merged

Thanks for your efforts to extend the support of the spark API!

[mariotaddeucci]

Hey @Tishj , I synced the branch but still getting the same error, now I don’t know what to do.

[Tishj]

Please look at the PR, it's not a function expression, it has its own method

[mariotaddeucci]

Got it, now it worked.
@Tishj thanks for all the support o/

[Tishj]

Thanks for the PR, in the future please try to not make unnecessary changes, like the formatting ;)

[Mytherin]

Could you just have a look at the merge conflicts?

[mariotaddeucci]

@Mytherin done o/

[Mytherin]

Thanks!