## What changes were proposed in this pull request?
This PR aims to add new **FoldablePropagation** optimizer that propagates foldable expressions by replacing all attributes with the aliases of original foldable expression. Other optimizations will take advantage of the propagated foldable expressions: e.g. `EliminateSorts` optimizer now can handle the following Case 2 and 3. (Case 1 is the previous implementation.)
1. Literals and foldable expression, e.g. "ORDER BY 1.0, 'abc', Now()"
2. Foldable ordinals, e.g. "SELECT 1.0, 'abc', Now() ORDER BY 1, 2, 3"
3. Foldable aliases, e.g. "SELECT 1.0 x, 'abc' y, Now() z ORDER BY x, y, z"
This PR has been generalized based on cloud-fan 's key ideas many times; he should be credited for the work he did.
**Before**
```
scala> sql("SELECT 1.0, Now() x ORDER BY 1, x").explain
== Physical Plan ==
WholeStageCodegen
: +- Sort [1.0#5 ASC,x#0 ASC], true, 0
: +- INPUT
+- Exchange rangepartitioning(1.0#5 ASC, x#0 ASC, 200), None
+- WholeStageCodegen
: +- Project [1.0 AS 1.0#5,1461873043577000 AS x#0]
: +- INPUT
+- Scan OneRowRelation[]
```
**After**
```
scala> sql("SELECT 1.0, Now() x ORDER BY 1, x").explain
== Physical Plan ==
WholeStageCodegen
: +- Project [1.0 AS 1.0#5,1461873079484000 AS x#0]
: +- INPUT
+- Scan OneRowRelation[]
```
## How was this patch tested?
Pass the Jenkins tests including a new test case.
Author: Dongjoon Hyun <dongjoon@apache.org>
Closes#12719 from dongjoon-hyun/SPARK-14939.
5907ebfc11