chore: replace unpkg with jsdelivr

[Rich-Harris]

I've found unpkg to be a bit flaky lately. It's completely unmaintained (last commit was three years ago). We should just use jsdelivr instead

[changeset-bot]

⚠️ No Changeset found

Latest commit: 4e842d6

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

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

[dummdidumm]

This won't suffice, it will fail on many packages, for example radix-svelte does work propertly on the current REPL but with this PR it fails. @PuruVJ said that unpkg does do some module resolution for packages that don't have an exports map etc, and that's missing in jsdelivr, so we would have to implement it ourselves.

[PuruVJ]

I added this line here in my original PR https://github.com/sveltejs/sites/pull/551/files#diff-292df1c211c573d5ee1e2b5a2caba399d3e405ad664c6fb99e28736dde95a80fR119-R136

I'm not sure whether its because of esm.run or jsdelivr. I remember one of these had the issue, so testing of that PR is needed to be fully sure

EDIT: It's JsDelivr