Default form wrapper in field widget is incorrect for cardinality > 1

Problem/Motivation

The default wrapper is set to 'item' which is semantically incorrect when the field is set to cardinality > 1 as the form is then set in a table. Furthermore, it throws off styling in claro theme as it tries to flex everything which breaks the the table layout.

Proposed resolution

Make default layout conditional in CustomWidgetBase so if cardinality is > 1, set to 'container'.