Raise Exception when awaiting JavaScript on auto-index page

[falkoschindler]

This PR tries to solve #2951 by preventing the user from awaiting any JavaScript call on the auto-index page.

As it turned out, many existing pytests had to be updated, since they didn't use page functions but awaited JavaScript.

There's a last problem with ui.notification, which currently can't be used on auto-index pages at all. It continuously checks if it is still contained in the DOM or if it should be deleted. With this PR in place, this check raises a RuntimeError.

Apart from ui.notification, the clipboard.read() function isn't usable on the auto-index page. Conceptually this is correct. But we will need to update corresponding demos which don't use page functions at the moment.

• update clipboard demos
• make ui.notification usable on auto-index page --> trigger event when notification disappears on one client and delete it for all others

[falkoschindler]

As a side effect of fixing the deletion of notifications in 5235446, we now can register "dismiss" events using the new on_dismiss parameter and pass JavaScript handlers for action buttons like this:

ui.notification('Hi!', close_button=True, on_dismiss=lambda: ui.notify('Dismissed'))
ui.notification('Ho!', actions=[{'label': 'Alert', ':handler': '() => alert("Alert!")'}])

[falkoschindler]

There seems to be a problem with codemirror, but I'm not sure if it's coming from this PR or the main branch. I'll look into it later.

[falkoschindler]

I think I fixed the problem in 154cb73.