## What changes were proposed in this pull request?
Add ```approxQuantile``` for SparkR.
## How was this patch tested?
unit tests

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #11383 from yanboliang/spark-13504 and squashes the following commits:

4f17adb [Yanbo Liang] Add approxQuantile for SparkR