Combined: Support adding the text content within the <footnotes> element + Drush upgrade path for 3x to 4x

This can be run via
```
drush footnotes:upgrade-3-to-4 node --use-data-text=false
```

Too many merge requests and conflicts to keep this sitting too long. If you have any subsequent issues please do raise a follow-up.
Thanks!

Automatically closed - issue fixed for 2 weeks with no activity.