New feature experimental_defaultFormStateBehavior.allOf added

@rjsf/mui

• fix gap in text and select widget outlines when "ui:label": false is specified.

@rjsf/utils

• Added an experimental flag allOf to experimental_defaultFormStateBehavior for populating defaults when using allOf schemas #3969

Dev / playground

• Added a dropdown for changing the experimental_defaultFormStateBehavior.allOf behaviour in the playground