fall back to native when printing an ExceptionGroup

[jakkdl]

Fixes #13753

I started looking into delving deeper into ultratb to add support for Exception Groups, but felt that this would be enough of an improvement over the status quo that it'd probably be worth implementing on it's own.
I also looked quite a bit at ipyparallel's CompositeError https://github.com/ipython/ipyparallel/blob/main/ipyparallel/error.py#L169, which seems like the equivalent of exception groups.

Remaining TODO:

• add tests
• add documentation

Will go ahead with those if the basic approach is deemed acceptable

[jakkdl]

I have no idea why the Run Downstream tests are failing, or if it's a problem in the PR. But otherwise everything passes, and docs & tests are written.

@Carreau would you mind reviewing?

[Carreau]

Apologies for the delay in reviewing I don't have much time on IPython.

Don't worry about the downstream failure.

[jakkdl]

No worries! I noticed you said the same in the other PRs so realized I should just go full steam ahead and implement the full PR so you only needed a single review pass :)