If there is only one bundle available, leave the default widget

Sorry for the commit guessing! Running a big migration script locally, didn't want to interrupt it with ddev router. This is now ready for review + has test coverage.

If only a single bundle is selected, the widget reverts to the default Core autocomplete. In addition to responding to any sort of alter, this has the additional benefit of making it easier to convert an existing site because autocomplete filters can just default to this widget with a sort of find and replace in form display config.

Great suggestion for improvement and good implementation.
Approved and merged.

Great thank you!

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