Add support for has(name, value) overload for URLSearchParams

[RoryDuncan]

The proxied URLSearchParams does not support the value parameter of the has method. Signature being has(name, value). You can see the first parameter—param—being the only forwarded argument in packages/kit/src/utils/url.js.

SvelteKit's URLSearchParams shares the same interface as mdn's URLSearchParams but its implementation differs.

As an example: Within a layout or page load function where a request has the url http://localhost:5173/?features=test.

export const load: LayoutLoad = ({ url }) => {
   url.searchParams.has("features"); // true
   url.searchParams.has("features", "test"); // true
   url.searchParams.has("features", "banners"); // true, incorrectly
   url.searchParams.has("features", "nonsense"); // true, incorrectly
   
   const searchParams = new URLSearchParams(url.href);
   searchParams.has("features"); // true
   searchParams.has("features", "test"); // true
   searchParams.has("features", "banners"); // false
   searchParams.has("features", "nonsense"); // false

   ...
}

Workaround

Creating a new URLSearchParams via the loader's url is a work-around.

Fix

Passing additional params in the proxy solves the issue.

1. In my changes, I'm uncertain if the search_params_callback signature should be changed to optionally have the value.
2. While the tests verify the changes work I am uncertain that adding a test for adherence to the browser interfaces is setting precedent for similar tests, and if that is out of intended scope for sveltekit's maintainers.

---

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with pnpm test and lint the project with pnpm lint and pnpm check

Changesets

• If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. Changesets that add features should be minor and those that fix bugs should be patch. Please prefix changeset messages with feat:, fix:, or chore:.

Edits

• Please ensure that 'Allow edits from maintainers' is checked. PRs without this option may be closed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 38d4ab5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[RoryDuncan]

Adding the changeset...

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

TIL this API exists 😆 Thanks! I'll rebase you on main after my fixes for the timing-out tests merges, then this should be good to go