[SPARK-21980][SQL] References in grouping functions should be indexed with semanticEquals

## What changes were proposed in this pull request?

https://issues.apache.org/jira/browse/SPARK-21980

This PR fixes the issue in ResolveGroupingAnalytics rule, which indexes the column references in grouping functions without considering case sensitive configurations.

The problem can be reproduced by:

`val df = spark.createDataFrame(Seq((1, 1), (2, 1), (2, 2))).toDF("a", "b")
 df.cube("a").agg(grouping("A")).show()`

## How was this patch tested?
unit tests

Author: donnyzone <[email protected]>

Closes apache#19202 from DonnyZone/ResolveGroupingAnalytics.

Author: DonnyZone

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

@@ -314,7 +314,7 @@ class Analyzer(
                 s"grouping columns (${groupByExprs.mkString(",")})")
           }
         case e @ Grouping(col: Expression) =>
-          val idx = groupByExprs.indexOf(col)
+          val idx = groupByExprs.indexWhere(_.semanticEquals(col))
           if (idx >= 0) {
             Alias(Cast(BitwiseAnd(ShiftRight(gid, Literal(groupByExprs.length - 1 - idx)),
               Literal(1)), ByteType), toPrettySQL(e))()

sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala

@@ -190,6 +190,22 @@ class DataFrameAggregateSuite extends QueryTest with SharedSQLContext {
     )
   }
 
+  test("SPARK-21980: References in grouping functions should be indexed with semanticEquals") {
+    checkAnswer(
+      courseSales.cube("course", "year")
+        .agg(grouping("CouRse"), grouping("year")),
+      Row("Java", 2012, 0, 0) ::
+        Row("Java", 2013, 0, 0) ::
+        Row("Java", null, 0, 1) ::
+        Row("dotNET", 2012, 0, 0) ::
+        Row("dotNET", 2013, 0, 0) ::
+        Row("dotNET", null, 0, 1) ::
+        Row(null, 2012, 1, 0) ::
+        Row(null, 2013, 1, 0) ::
+        Row(null, null, 1, 1) :: Nil
+    )
+  }
+
   test("rollup overlapping columns") {
     checkAnswer(
       testData2.rollup($"a" + $"b" as "foo", $"b" as "bar").agg(sum($"a" - $"b") as "foo"),