[SPARK-23501][UI] Refactor AllStagesPage in order to avoid redundant code

As suggested in #20651, the code is very redundant in `AllStagesPage` and modifying it is a copy-and-paste work. We should avoid such a pattern, which is error prone, and have a cleaner solution which avoids code redundancy.

existing UTs

Author: Marco Gaido <marcogaido91@gmail.com>

Closes #20663 from mgaido91/SPARK-23475_followup.