[SPARK-23908][SQL] Add transform function.

[ueshin]

What changes were proposed in this pull request?

This pr adds transform function which transforms elements in an array using the function.
Optionally we can take the index of each element as the second argument.

>SELECT transform(array(1, 2, 3), x -> x +1);
array(2, 3, 4)
>SELECT transform(array(1, 2, 3), (x, i) -> x + i);
array(1, 3, 5)

How was this patch tested?

Added tests.