Messages: New privacy preference

In the app, login in a 3.5 site or older. Go to App Settings > Message preferences. Check that you see a toggle for the setting "prevent non-contacts from messaging me", like it's been in the app so far. Check that you can change the setting. In web, login as admin in a Moodle with master branch.  Enable 'Enable users to message anyone' ($CFG->messagingallusers) in 'Site Administration | Advanced Features'. In the app, login in that site and go to App Settings > Message preferences. Check that you see a setting "Accept messages from" instead of the block non-contacts one, and it has 3 options. Check that you can change the setting successfully. You can login in web with the same user and check that the setting is updated in there if you change it in the app. Back in web as admin, disable 'Enable users to message anyone' . Restart the app and go back to Message preferences. Check that now you only see 2 options, you shouldn't see the option "Anyone on the site".