Allow backtracking to previous group when current group is invalid

[cpcf]

Is your feature request related to a problem? Please describe.

Currently, if the active group in a form has an error, the user is blocked from navigating to a previous group. This can be problematic when resolving the error requires changes to an earlier group.

For example, in the burger example, if I'm entering an order for Frank and encounter a validation issue in the name section, I might decide to go back and change the order for someone else. However, pressing Shift+Tab softlocks the form, preventing backtracking.

Maybe this is intentional, but I’d expect to be able to navigate backward even if the current group has validation issues.

Describe the solution you'd like

Introduce an option to control the strictness of group backtracking. This setting would allow users to override the default behavior, enabling navigation to previous groups even when errors exist in the current group.

Describe alternatives you've considered

Right now, I have to structure forms so that each group is entirely self-contained. This results in overloaded groups and a worse user experience.

Additional context

This issue is especially problematic for field_confirm. If a later group includes a confirmation box and the selected value fails validation, the user is stuck, unable to navigate back to previous groups until they have set the confirm to a valid value.
See: #541