Have enhanced form action responses use HTTP status codes returned from fail

[theetrain]

Describe the problem

When using <form use:enhance> to send an enhanced form action request, client-side fetch is used to request data from SvelteKit that currently is always returned with status code 200 even when return fail(400, {}) is used.

This is problematic when trying to track responses with a status of 400 (for example) using observability tools like Sentry.

Describe the proposed solution

Have the HTTP status code in a form action response match the status code of either return {} (200 or 204), or match the status code returned from fail().

This way, I can more easily track which user received which status code using observability tools. Due to the change in behaviour, I'd consider this a breaking change to SvelteKit if we proceed.

Alternatives considered

Manually log responses client-side based on response.status in use:enhance.

Importance

would make my life easier

Additional Information

Continued from: #7233 (comment)