[SPARK-28199][SS][FOLLOWUP] Remove package private in class/object in…

… sql.execution package

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

This PR proposes to remove package private in classes/objects in sql.execution package, as per SPARK-16964.

### Why are the changes needed?

This is per post-hoc review comment, see apache#24996 (comment)

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

No.

### How was this patch tested?

N/A

Closes apache#28790 from HeartSaVioR/SPARK-28199-FOLLOWUP-apply-SPARK-16964.

Authored-by: Jungtaek Lim (HeartSaVioR) <kabhwan.opensource@gmail.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/Triggers.scala

@@ -50,17 +50,17 @@ private object Triggers {
  * A [[Trigger]] that processes only one batch of data in a streaming query then terminates
  * the query.
  */
-private[sql] case object OneTimeTrigger extends Trigger
+case object OneTimeTrigger extends Trigger
 
 /**
  * A [[Trigger]] that runs a query periodically based on the processing time. If `interval` is 0,
  * the query will run as fast as possible.
  */
-private[sql] case class ProcessingTimeTrigger(intervalMs: Long) extends Trigger {
+case class ProcessingTimeTrigger(intervalMs: Long) extends Trigger {
   Triggers.validate(intervalMs)
 }
 
-private[sql] object ProcessingTimeTrigger {
+object ProcessingTimeTrigger {
   import Triggers._
 
   def apply(interval: String): ProcessingTimeTrigger = {
@@ -84,11 +84,11 @@ private[sql] object ProcessingTimeTrigger {
  * A [[Trigger]] that continuously processes streaming data, asynchronously checkpointing at
  * the specified interval.
  */
-private[sql] case class ContinuousTrigger(intervalMs: Long) extends Trigger {
+case class ContinuousTrigger(intervalMs: Long) extends Trigger {
   Triggers.validate(intervalMs)
 }
 
-private[sql] object ContinuousTrigger {
+object ContinuousTrigger {
   import Triggers._
 
   def apply(interval: String): ContinuousTrigger = {