[SPARK-16044][SQL] input_file_name() returns empty strings in data sources based on NewHadoopRDD

## What changes were proposed in this pull request?

This PR makes `input_file_name()` function return the file paths not empty strings for external data sources based on `NewHadoopRDD`, such as [spark-redshift](https://github.com/databricks/spark-redshift/blob/cba5eee1ab79ae8f0fa9e668373a54d2b5babf6b/src/main/scala/com/databricks/spark/redshift/RedshiftRelation.scala#L149) and [spark-xml](https://github.com/databricks/spark-xml/blob/master/src/main/scala/com/databricks/spark/xml/util/XmlFile.scala#L39-L47).

The codes with the external data sources below:

```scala
df.select(input_file_name).show()
```

will produce

- **Before**
  ```
+-----------------+
|input_file_name()|
+-----------------+
|                 |
+-----------------+
```

- **After**
  ```
+--------------------+
|   input_file_name()|
+--------------------+
|file:/private/var...|
+--------------------+
```

## How was this patch tested?

Unit tests in `ColumnExpressionSuite`.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #13759 from HyukjinKwon/SPARK-16044.