fix: add migration task when there's a variable named that would conflict with a rune

[paoloricciuti]

Closes #14215

As usual with the migration script you start simple and then you realise new edge cases. This started simply with a state variable erroring when migrating to $state. Then i realised the same could be true for $derived and $props and $bindable.

There are some false negative here: technically this is migratable

<script>
    export let props;
</script>

because

<script>
    let { props } = $props();
</script>

is valid but while with props is probably fine trying to migrate when the binding is in the expression that we are migrating is a lot more complex for derived for example (because we create some new derived in some cases and we don't have a node for that. But i would say this is still good enough and better have some false negative for an edge case than migrate something that can break imho.

There are a lot of tests but that's because i couldn't test multiple things in the same test :(

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
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests and linting

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

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@14216

[changeset-bot]

🦋 Changeset detected

Latest commit: 9a575e6

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

This PR includes changesets to release 1 package

Name	Type
svelte	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