Corpus: update domain when changing used text features

[ajdapretnar]

Describe the bug
Apparently, Corpus never updated the output domain, when the user changed the used text features list.

To Reproduce
Steps to reproduce the behavior:

1. Corpus, load grimms-tales-selected.
2. Changed the used text feature to Abstract.
3. Inspect the output domain with Python Script. Or try to save the Corpus with Save Data. You will see Abstract is never registered as used text feature.

Expected behavior
The user can save the corpus exactly as it is presented in the widget.

Orange version:
3.36.dev

Text add-on version:
1.14.dev

Additional context
Updating the domain would help us get rid of Corpus properties, which is an additional bonus.
ATM, the workaround for the bug is using Edit Domain (less elegant and not as intuitive).