Allow preventing form submission events

[daun]

Description

• Check for prevented submit events before submitting forms
• Allow preventing form submission using standard event handling
• Work in progress

Example usage

swup.hooks.before('form:submit', (visit, { el: form, event }) => {
  if (form.dataset.submitting) {
    event.preventDefault()
  }
  form.dataset.submitting = true
})

Checks

• The PR is submitted to the main branch
• The code was linted before pushing (npm run lint)
• All tests are passing (npm run test)
• New or updated tests are included
• The documentation was updated as required

Additional information

• Closes [Bug]: Unintentional consecutive form submissions #81