[SPARK-18555][SQL] DataFrameNaFunctions.fill miss up original values in long integers

## What changes were proposed in this pull request?

   DataSet.na.fill(0) used on a DataSet which has a long value column, it will change the original long value.

   The reason is that the type of the function fill's param is Double, and the numeric columns are always cast to double(`fillCol[Double](f, value)`) .
```
  def fill(value: Double, cols: Seq[String]): DataFrame = {
    val columnEquals = df.sparkSession.sessionState.analyzer.resolver
    val projections = df.schema.fields.map { f =>
      // Only fill if the column is part of the cols list.
      if (f.dataType.isInstanceOf[NumericType] && cols.exists(col => columnEquals(f.name, col))) {
        fillCol[Double](f, value)
      } else {
        df.col(f.name)
      }
    }
    df.select(projections : _*)
  }
```

 For example:
```
scala> val df = Seq[(Long, Long)]((1, 2), (-1, -2), (9123146099426677101L, 9123146560113991650L)).toDF("a", "b")
df: org.apache.spark.sql.DataFrame = [a: bigint, b: bigint]

scala> df.show
+-------------------+-------------------+
|                  a|                  b|
+-------------------+-------------------+
|                  1|                  2|
|                 -1|                 -2|
|9123146099426677101|9123146560113991650|
+-------------------+-------------------+

scala> df.na.fill(0).show
+-------------------+-------------------+
|                  a|                  b|
+-------------------+-------------------+
|                  1|                  2|
|                 -1|                 -2|
|9123146099426676736|9123146560113991680|
+-------------------+-------------------+
 ```

the original values changed [which is not we expected result]:
```
 9123146099426677101 -> 9123146099426676736
 9123146560113991650 -> 9123146560113991680
```

## How was this patch tested?

unit test added.

Author: root <root@iZbp1gsnrlfzjxh82cz80vZ.(none)>

Closes #15994 from windpiger/nafillMissupOriginalValue.

(cherry picked from commit 508de38c)
Signed-off-by: DB Tsai <dbtsai@dbtsai.com>