[SPARK-16289][SQL] Implement posexplode table generating function

## What changes were proposed in this pull request?

This PR implements `posexplode` table generating function. Currently, master branch raises the following exception for `map` argument. It's different from Hive.

**Before**
```scala
scala> sql("select posexplode(map('a', 1, 'b', 2))").show
org.apache.spark.sql.AnalysisException: No handler for Hive UDF ... posexplode() takes an array as a parameter; line 1 pos 7
```

**After**
```scala
scala> sql("select posexplode(map('a', 1, 'b', 2))").show
+---+---+-----+
|pos|key|value|
+---+---+-----+
|  0|  a|    1|
|  1|  b|    2|
+---+---+-----+
```

For `array` argument, `after` is the same with `before`.
```
scala> sql("select posexplode(array(1, 2, 3))").show
+---+---+
|pos|col|
+---+---+
|  0|  1|
|  1|  2|
|  2|  3|
+---+---+
```

## How was this patch tested?

Pass the Jenkins tests with newly added testcases.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #13971 from dongjoon-hyun/SPARK-16289.

1 files changed, 1 insertions, 0 deletions

diff --git a/R/pkg/NAMESPACE b/R/pkg/NAMESPACE
index e0ffde922d..abc65887bc 100644
--- a/R/pkg/NAMESPACE
+++ b/R/pkg/NAMESPACE
@@ -234,6 +234,7 @@ exportMethods("%in%",
               "over",
               "percent_rank",
               "pmod",
+              "posexplode",
               "quarter",
               "rand",
               "randn",