[SPARK-19314][SS][CATALYST] Do not allow sort before aggregation in Structured Streaming plan

## What changes were proposed in this pull request?

Sort in a streaming plan should be allowed only after a aggregation in complete mode. Currently it is incorrectly allowed when present anywhere in the plan. It gives unpredictable potentially incorrect results.

## How was this patch tested?
New test

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #16662 from tdas/SPARK-19314.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/UnsupportedOperationChecker.scala

@@ -87,7 +87,7 @@ object UnsupportedOperationChecker {
      * data.
      */
     def containsCompleteData(subplan: LogicalPlan): Boolean = {
-      val aggs = plan.collect { case a@Aggregate(_, _, _) if a.isStreaming => a }
+      val aggs = subplan.collect { case a@Aggregate(_, _, _) if a.isStreaming => a }
       // Either the subplan has no streaming source, or it has aggregation with Complete mode
       !subplan.isStreaming || (aggs.nonEmpty && outputMode == InternalOutputModes.Complete)
     }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/UnsupportedOperationsSuite.scala

@@ -199,12 +199,17 @@ class UnsupportedOperationsSuite extends SparkFunSuite {
     _.intersect(_),
     streamStreamSupported = false)
 
-  // Sort: supported only on batch subplans and on aggregation + complete output mode
+  // Sort: supported only on batch subplans and after aggregation on streaming plan + complete mode
   testUnaryOperatorInStreamingPlan("sort", Sort(Nil, true, _))
   assertSupportedInStreamingPlan(
-    "sort - sort over aggregated data in Complete output mode",
+    "sort - sort after aggregation in Complete output mode",
     streamRelation.groupBy()(Count("*")).sortBy(),
     Complete)
+  assertNotSupportedInStreamingPlan(
+    "sort - sort before aggregation in Complete output mode",
+    streamRelation.sortBy().groupBy()(Count("*")),
+    Complete,
+    Seq("sort", "aggregat", "complete"))
   assertNotSupportedInStreamingPlan(
     "sort - sort over aggregated data in Update output mode",
     streamRelation.groupBy()(Count("*")).sortBy(),