[SPARK-14830][SQL] Add RemoveRepetitionFromGroupExpressions optimizer.
## What changes were proposed in this pull request?
This PR aims to optimize GroupExpressions by removing repeating expressions. `RemoveRepetitionFromGroupExpressions` is added.
**Before**
```scala
scala> sql("select a+1 from values 1,2 T(a) group by a+1, 1+a, A+1, 1+A").explain()
== Physical Plan ==
WholeStageCodegen
: +- TungstenAggregate(key=[(a#0 + 1)#6,(1 + a#0)#7,(A#0 + 1)#8,(1 + A#0)#9], functions=[], output=[(a + 1)#5])
: +- INPUT
+- Exchange hashpartitioning((a#0 + 1)#6, (1 + a#0)#7, (A#0 + 1)#8, (1 + A#0)#9, 200), None
+- WholeStageCodegen
: +- TungstenAggregate(key=[(a#0 + 1) AS (a#0 + 1)#6,(1 + a#0) AS (1 + a#0)#7,(A#0 + 1) AS (A#0 + 1)#8,(1 + A#0) AS (1 + A#0)#9], functions=[], output=[(a#0 + 1)#6,(1 + a#0)#7,(A#0 + 1)#8,(1 + A#0)#9])
: +- INPUT
+- LocalTableScan [a#0], [[1],[2]]
```
**After**
```scala
scala> sql("select a+1 from values 1,2 T(a) group by a+1, 1+a, A+1, 1+A").explain()
== Physical Plan ==
WholeStageCodegen
: +- TungstenAggregate(key=[(a#0 + 1)#6], functions=[], output=[(a + 1)#5])
: +- INPUT
+- Exchange hashpartitioning((a#0 + 1)#6, 200), None
+- WholeStageCodegen
: +- TungstenAggregate(key=[(a#0 + 1) AS (a#0 + 1)#6], functions=[], output=[(a#0 + 1)#6])
: +- INPUT
+- LocalTableScan [a#0], [[1],[2]]
```
## How was this patch tested?
Pass the Jenkins tests (with a new testcase)
Author: Dongjoon Hyun <dongjoon@apache.org>
Closes #12590 from dongjoon-hyun/SPARK-14830.
6e6320122e