Add 'title' to field config to use as default for widget config

Updated issue summary to reflect using the new approach - instead of moving the attribute from widget to field config, the widget config is being retained but uses the field attribute as its default.

Note because we're keeping the attribute on the widget config, there is no need for an upgrade path here.

I think the current state of MR15 is functionally complete; however we currently have no tests for the autocomplete widget, and we need to use FunctionalJavascript to test the Ajax. I need to get that working on my local dev env which doesn't look to be that straightforward on ddev so spinning up Lando for a play.

Merge conflicts to 2.0.x resolved.

Have created 📌 Add tests for the autocomplete widget Active for the autocomplete tests, so as to not hold back this issue.

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