## 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.
```sql
> 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.
Author: Takuya UESHIN <ueshin@databricks.com>
Closes#21954 from ueshin/issues/SPARK-23908/transform.
02f967795b