Add functions.transform

[timsaucer]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

This is related to #807 but slightly different. As a user I want to be able to apply a transform function to every element of an array. Suppose I have a dataframe where one column contains an array.

DataFrame()
+-----------+
| a         |
+-----------+
| [1, 2, 3] |
| [4, 5]    |
| [6]       |
| []        |
+-----------+

I might want to convert this with a single line such that each element is converted to whether it is odd.

DataFrame()
+---------------------+
| a_odd               |
+---------------------+
| [True, False, True] |
| [False, True]       |
| [False]             |
| []                  |
+---------------------+

It would be great to do something like datafusion.functions.transform(col("a"), my_func).alias("a_odd")

Describe the solution you'd like

Right now I'm not completely sure how I would do this. I think I might have to do an unnest, transform, and aggregate.

Describe alternatives you've considered

These could be done with a UDF.

Additional context