Do not lock the instance settings for the Entity Reference field

When a new entity queue is created, a "locked" instance of an entity reference field is created. I'm guessing the locked state is specified because Entity Queue depends on that field, but it prevents other settings from being modified, such as the width of the autocomplete textfield, the label, help text, and how autocomplete functionality works.

I'd also like to make the widget settings modifiable so that #2928765: Add items to top of the queue instead of the bottom would be possible. It would also be a prerequisite for #2342843: Allow a per-queue view for Entity Reference autocomplete, if that ever becomes an option in Entity Reference module.