chore: service worker as a Vite environment

[teemingc]

This PR refactors the service worker code so that it utilises the Vite environment API. This means it:

• can have its own Vite config options instead of sharing them with the client environment.
• it's a lot easier to detect invalid module imports and throw an error since it'll always be in the service worker environment if it does happen

This PR also does a little cleanup such as:

• moving those applyEnvironment hooks below the config hook since they only get applied after them (therefore, applyEnvironment does not influence whether config is run.)
• moving service worker related stuff to the service worker plugin

---

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]

⚠️ No Changeset found

Latest commit: 97badda

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

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-15614-svelte.vercel.app/

[teemingc]

This fixes a type issue where you can't specify options unless you specifically set register: true although that's the default

[teemingc]

We don't need this test anymore because we're not proxying the worker. We're transforming the entry file using the service worker environment and returning the transformed code.