Bugfix/view modes and card view

[i-just]

Description

Issue 1:
Sources only had the view modes if they were considered top-level sources. While that’s fine for the CMS itself, the Commerce Orders do use nested sources (e.g. All Orders > New). Not having the view modes available for non-top-level sources triggered JS errors and caused the non-top-level index page not to work as expected.

Solution:

• Added additional safeguards to stop assuming that sourceViewModes will always be defined and contain anything.
• The data-view-modes attribute is now populated for the non-top-level sources, too

Issue 2:
An error was thrown when a native field was dragged into the field layout designer and selected to be included in the card view straight away.

Solution:
Added craft\fieldlayoutelements\BaseField::previewPlaceholderHtml().

Issue 3:
When a field was dragged into the field layout designer, a corresponding checkbox was added under “Card Attributes” straight away. No checks were made to see if that field was previewable.

Solution:
Added extra checks to ensure the field is previewable before adding/removing a corresponding checkbox on the fly.

Issue 4:
When a field that was selected to show on the card was removed from the designer, the card preview was not updated accordingly.

Solution:
Uncheck the checkbox before removal.

Issue 5:
When a field that was selected to provide a thumbnail for the card was removed from the designer, the card preview was not updated accordingly.

Solution:
Set the card view designer to now show a thumbnail and update the preview.

Related issues

n/a