fix: Stop re-loading already-loaded CSS during server-side route resolution

[elliott-with-the-longest-name-on-github]

Changes:

• In load_css, grab the existing links' href attributes, which are absolute URLs to the CSS asset, and store them in a set
• When checking to see if a link for an asset exists, first, resolve it as an absolute URL before checking that it exists in the set

I also switched the tests to use page.locactor, which will poll until the default timeout to see if something has changed. This needs to happen prior to checking the array. We really should use page.locator rather than page.textContent in general.

Observed behavior before this PR:

Basically, on server-side route resolution, load_css is re-loading CSS modules that are already in the document. You can see the behavior on pnpm -F test-basics build && pnpm -F test-basics preview by visiting http://localhost:4173/routing/form-get. Check the network requests for CSS, then type something into the input and click "submit". You'll see the CSS get loaded again.

Tracing, the problem here is:

The initial load includes these links in the head:

<link href="../_app/immutable/assets/0.DylTJ_5d.css" rel="stylesheet">
<link rel="stylesheet" crossorigin="" href="http://localhost:4173/_app/immutable/assets/1.CDE3T0tB.css">

On submission, the __route.js file returns this line:

import('../../_app/immutable/entry/start.D96TxtfR.js').then(x => x.load_css(['/_app/immutable/assets/1.CDE3T0tB.css','/_app/immutable/assets/0.DylTJ_5d.css',]));

load_css looks like this:

export function load_css(deps) {
	if (__SVELTEKIT_CLIENT_ROUTING__) return;

	const csp_nonce_meta = /** @type {HTMLMetaElement} */ (
		document.querySelector('meta[property=csp-nonce]')
	);
	const csp_nonce = csp_nonce_meta?.nonce || csp_nonce_meta?.getAttribute('nonce');

	for (const dep of deps) {
		if (dep in seen) continue;
		seen[dep] = true;
		if (document.querySelector(`link[href="${dep}"][rel="stylesheet"]`)) {
			continue;
		}

		const link = document.createElement('link');
		link.rel = 'stylesheet';
		link.crossOrigin = '';
		link.href = dep;
		if (csp_nonce) {
			link.setAttribute('nonce', csp_nonce);
		}
		document.head.appendChild(link);
	}
}

So it sees the following two deps:

/_app/immutable/assets/0.DylTJ_5d.css
/_app/immutable/assets/1.CDE3T0tB.css

However, the selector doesn't match, because the 0 href is relative.

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Latest commit: e87bf77

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