[SPARK-43063][SQL][FOLLOWUP] Add ToPrettyString expression for Dataset.show

### What changes were proposed in this pull request?

This is a followup of apache#40699 to avoid changing the Cast behavior. It pulls out the cast-to-string code into a base trait, and add a new Expression `ToPrettyString` to extend this trait with a little customization.

It also handles binary value inside array/struct/map to also print hex format, for `df.show` only, not `Cast`.

### Why are the changes needed?

avoid behavior change

### Does this PR introduce _any_ user-facing change?

change back the behavior of casting array/map/struct to string regarding null elements. It was `null`, then changed to `NULL` in apache#40699 , and is `null` again after this PR.

### How was this patch tested?

existing tests

Closes apache#40922 from cloud-fan/pretty.

Authored-by: Wenchen Fan <[email protected]>
Signed-off-by: Wenchen Fan <[email protected]>

Author: cloud-fan