Support uncertainties as EA Dtype
In parallel with Pint and Pint-Pandas, changes to support uncertainties as an EA Dtype.

See https://github.com/hgrecco/pint/pull/1615
and https://github.com/hgrecco/pint-pandas/pull/140

- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

IIUC the problem here is isna not recognizing your custom scalar?  I think the way to address this is directly in #27462/#27825

My last attempt at an implementation was #51378, which I still think is the way to go. Please consider adding the https://github.com/pandas-dev/pandas/milestone/103 label to this pull-request.  There should be no user-visible changes.  The 2.1 milestone contains several enhancements that would further enhance the development versions of Pint and Pint-Pandas which await the changes from this pull request (see https://github.com/hgrecco/pint/pull/1615 and https://github.com/hgrecco/pint-pandas/pull/140). Looks like we now depend on https://github.com/pandas-dev/pandas/pull/54110 for CI/CD to pass (which is not yet merged). I also don't understand this complaint from `pylint`:

```
pylint...................................................................Failed
- hook id: pylint
- duration: 793.25s
- exit code: 4

************* Module pandas.tests.extension.json.test_json
pandas/tests/extension/json/test_json.py:[359](https://github.com/pandas-dev/pandas/actions/runs/5553184370/jobs/10141428866?pr=53970#step:12:364):4: W0246: Useless parent or super() delegation in method 'test_groupby_agg_extension' (useless-parent-delegation)
```

The code I un-commented was original code, and it appears to follow precisely the pattern of all other code in the module.  I'm at a loss as to how to proceed because I didn't create the `TestGroupby` class hierarchy and don't know why this particular case is getting singled out. > The code I un-commented was original code

Again, just remove it and the parent class test will run. > > The code I un-commented was original code
> 
> Again, just remove it and the parent class test will run.

Ah, now I understand.  I was afraid to remove a test that should be run, and did not grok that the test would run in the parent class.  I'll re-submit, waiting a few hours in case there's an answer to my pyarrow question. This PR is obsolete now.