Event instances created using the Add Instance feature don't have inheritance enabled by default

Problem/Motivation

When adding an instance using the Add Instance tab on an event series, the created instance doesn't have field inheritance enabled by default. Thus, the title, description, and other values that should be inherited from the series do not appear on the new instance.

This can be particularly confusing to non-admin authors because the Field Inheritance field is not enabled out-of-the-box on the event instance form, so there's nothing to indicate why the values are not inheriting the way they do on other instances in the series, and no option to fix it.

Steps to reproduce

1. Log in and go to /events/add/default.
2. Set Frequency to Daily, then set the start and end dates so that the event repeats for several days.
3. Fill in all other required fields and Save.
4. Click the Add Instance tab.
5. Set the start and end fields, leave all other fields unset, and click Save.

Expected result: The event series title and description show on the newly added event instance.
Actual result: The series title and description do not display.

If you then go to /admin/structure/events/instance/types/eventinstance_type/default/edit/form-display and add the Field Inheritance field to the form, then edit the newly added event instance, you'll see that the "Enable inheritance for this entity?" checkbox is unchecked.

Proposed resolution

Instances created using Add Instance should have field inheritance enabled by default, the same way that the instances that were created by the series' recurrence pattern do. Pretty sure this was the case with 2.x, but seems to have been lost with 3.x.