## What changes were proposed in this pull request?
It's the follow-up PR for #22962, contains the following works:
- Remove `__init__` in TaskContext and BarrierTaskContext.
- Add more comments to explain the fix.
- Rewrite UT in a new class.
## How was this patch tested?
New UT in test_taskcontext.py
Closes#23435 from xuanyuanking/SPARK-25921-follow.
Authored-by: Yuanjian Li <xyliyuanjian@gmail.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>