ENH: implement FloatingArray.round()
- [x] closes #38844
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
milestoned as 1.2.1. ok to merge changes to experimental types in patch releases? these generally should not be backported as EAs (esp) Floating are still experimental > milestoned as 1.2.1. ok to merge changes to experimental types in patch releases?

we can do on a case by case. the proposed fix here that i suggest is a bit more non-trivial. Since I think being able to round is a quite essential functionality for a floating dtypes that we missed, I think it makes sense to backport this, exactly because it is still experimental anyway. 
(since it's experimental anyway, we don't need to be as careful to backport as for other parts of pandas, and by backporting this, it will make it easier for users to actually already experiment with the new dtype in pandas 1.2.x, and thus we can get more feedback) > Since I think being able to round is a quite essential functionality for a floating dtypes that we missed, I think it makes sense to backport this, exactly because it is still experimental anyway.
> (since it's experimental anyway, we don't need to be as careful to backport as for other parts of pandas, and by backporting this, it will make it easier for users to actually already experiment with the new dtype in pandas 1.2.x, and thus we can get more feedback)

I don't think we should be backporting things like this. This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. closing as stale. I think we need the general soln outlined above. Happy to re-open / take new PR.