As of #23867 this is now a real package, so updating the imports to
use the real package name, rather than relying on the alias. The
name change in the package name is because `I18n` is not a valid
name as NPM packages must be all lowercase.
This commit also introduces an eslint rule to prevent importing from
the old I18n path.
For themes/plugins, the old 'i18n' name remains functional.
1. The events table had broken styling, making each row overflow
2. It had confusing routes: `/:id` for "edit" and `/:id/events` for "show" (now it's `/:id/edit` and `/:id` respectively)
3. There previously was an unused backend action (`#edit`) - now it is used (and `web_hooks/:id/events` route has been removed)
4. There was outdated/misplaced/duplicated CSS
5. And more
