This is running into various problems with invalid assumptions about asyncio in the script magics (#13348)

In two commits because the first commit should be backported to 7.x, while the second is only for the 8.0 updates to script magics.

FWIW, referring to the Python patch deprecating get_event_loop, it is an accident that policy.get_event_loop is not also deprecated. So this and #13289 is only an extremely temporary measure.

We should move to our own handle on the event loop, and remove all calls to get_event_loop and set_event_loop (including the policy methods). That should be 8.0-only, I think.

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 7.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -m1 e343cd4e5872a1fef8ba7f7d111f37315e21cd28

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #13349: get_running_loop is only valid in coroutines'

4. Push to a named branch:

git push YOURFORK 7.x:auto-backport-of-pr-13349-on-7.x

5. Create a PR against branch 7.x, I would have named this PR:

"Backport PR #13349 on branch 7.x (get_running_loop is only valid in coroutines)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.