[SPARK-18720][SQL][MINOR] Code Refactoring of withColumn

### What changes were proposed in this pull request?
Our existing withColumn for adding metadata can simply use the existing public withColumn API.

### How was this patch tested?
The existing test cases cover it.

Author: gatorsmile <gatorsmile@gmail.com>

Closes #16152 from gatorsmile/withColumnRefactoring.