Improve error messages on required fields when they're hidden by Javascript states

Problem/Motivation

🐛 Regression from #3341682: #states + #required do not automatically work together, resulting in an unsubmittable AccountSettingsForm Fixed revealed that a required field hidden by #state isn't visible to the user so it's not clear what is wrong to the user.

Steps to reproduce

Install umami
Visit en/admin/config/people/accounts
In the 'Account activation' tab, empty the subject field and then untick 'Notify user when account is activated'
Save the form and note the error message 'This value should not be blank' but observe that neither the vertical tab or the invalid field can be easily found.

Proposed resolution

If a field is invalid, but hidden by #states, make it visible

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet