[SPARK-19727][SQL] Fix for round function that modifies original column

## What changes were proposed in this pull request?

Fix for SQL round function that modifies original column when underlying data frame is created from a local product.

    import org.apache.spark.sql.functions._

    case class NumericRow(value: BigDecimal)

    val df = spark.createDataFrame(Seq(NumericRow(BigDecimal("1.23456789"))))

    df.show()
    +--------------------+
    |               value|
    +--------------------+
    |1.234567890000000000|
    +--------------------+

    df.withColumn("value_rounded", round('value)).show()

    // before
    +--------------------+-------------+
    |               value|value_rounded|
    +--------------------+-------------+
    |1.000000000000000000|            1|
    +--------------------+-------------+

    // after
    +--------------------+-------------+
    |               value|value_rounded|
    +--------------------+-------------+
    |1.234567890000000000|            1|
    +--------------------+-------------+

## How was this patch tested?

New unit test added to existing suite `org.apache.spark.sql.MathFunctionsSuite`

Author: Wojtek Szymanski <wk.szymanski@gmail.com>

Closes #17075 from wojtek-szymanski/SPARK-19727.