Bug 2676 pre submit custom validation v1

[ehenighan]

Description

Separated 'should include in form submission' from 'should validate as part of form submission' to ensure custom validation hooks are still evaluated on unchecked checkboxes and radiogroups without a selection.

Corresponding issue: https://github.com/bigskysoftware/htmx/issues/2676

Testing

Tested manually using the replication sample attached to the ticket. Added automated tests without the fix to demonstrate the problem, and then restored the fix and checked that the failing tests now passed.

Checklist

• [X] I have read the contribution guidelines
• [X] I have targeted this PR against the correct branch (master for website changes, dev for source changes)
• [X] This is either a bugfix, a documentation update, or a new feature that has been explicitly approved via an issue
• [X] I ran the test suite locally (npm run test) and verified that it succeeded