[SPARK-29870][SQL][FOLLOW-UP] Keep CalendarInterval's toString

[HyukjinKwon]

What changes were proposed in this pull request?

This is a followup of #26418. This PR removed CalendarInterval's toString with an unfinished changes.

Why are the changes needed?

1. Ideally we should make each PR isolated and separate targeting one issue without touching unrelated codes.

2. There are some other places where the string formats were exposed to users. For example:

   scala> sql("select interval 1 days as a").selectExpr("to_csv(struct(a))").show()

   +--------------------------+
   |to_csv(named_struct(a, a))|
   +--------------------------+
   |      "CalendarInterval...|
   +--------------------------+
   

3. Such fixes:

    private def writeMapData(
       map: MapData, mapType: MapType, fieldWriter: ValueWriter): Unit = {
     val keyArray = map.keyArray()
   + val keyString = mapType.keyType match {
   +   case CalendarIntervalType =>
   +    (i: Int) => IntervalUtils.toMultiUnitsString(keyArray.getInterval(i))
   +   case _ => (i: Int) => keyArray.get(i, mapType.keyType).toString
   + }

   can cause performance regression due to type dispatch for each map.

Does this PR introduce any user-facing change?

Yes, see 2. case above.

How was this patch tested?

Manually tested.

[HyukjinKwon]

cc @cloud-fan and @yaooqinn

[yaooqinn]

LGTM, thanks for your follow-up.

[cloud-fan]

probably add a comment saying that the toString implementation is the multi-units format.

[SparkQA]

Test build #114009 has finished for PR 26572 at commit 81e8deb.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

This doesn't change behavior, right? same string comes out?

[HyukjinKwon]

Yup, as it will still call toString.

[HyukjinKwon]

Last commit is comment-only (eefd457).
I locally checked ./dev/lint-scala which is only related to this change.

[HyukjinKwon]

Merged to master.