feat: allow to opt-out of use:enhance for forms

[fehnomenal]

fix #13180

I reused the data-sveltekit-reload attribute to opt-out of use:enhance. The attribute can be present either on the form element or the form button.

More details of the reasoning in the linked issue but tl;dr: I need to post to an endpoint in a new tab from the same form that is used for formactions and use:enhance.

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[Rich-Harris]

preview: https://svelte-dev-git-preview-kit-13250-svelte.vercel.app/

this is an automated message

[eltigerchino]

I wonder if we can reuse the get_router_options function to get the reload option state

kit/packages/kit/src/runtime/client/utils.js

Line 151 in 9a4a411

export function get_router_options(element) {

[fehnomenal]

I also thought about reusing it but decided against it as I think it could result in surprising and hard to debug code if the parents of two elements (the form and the button) are inspected for the reload option.

Instead I reused the underlying functions and logic.