feat: allow $state in return statements

[Ocean-OS]

This allows $state calls to be returned from a function, returning a proxy (if the argument can be proxied). This has been mentioned a few times, but I can't find the issues. I don't know if we should warn on arguments that aren't proxiable, I'm leaning towards 'no' since that would probably be unnecessary.

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.
• If this PR changes code within packages/svelte/src, add a changeset (npx changeset).

Tests and linting

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

[changeset-bot]

🦋 Changeset detected

Latest commit: e13c7d9

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

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-15589-svelte.vercel.app/

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@15589

[naylour]

Yes

[Ocean-OS]

I'm not sure if this should also apply to implicit returns in arrow functions, does anyone have any input on that?

[benmccann]

it would be good to have a test, which would also help illuminate what is being supported

[benmccann]

I believe new features are normally considered a minor release

Suggested change

	'svelte': patch
	'svelte': minor

[Ocean-OS]

it would be good to have a test, which would also help illuminate what is being supported

I'll add the test in a bit. This PR allows you to return a $state call, like so:

function fn() {
    //...
    return $state(obj); 
} 

In this example, $state gets compiled to $.proxy, proxying the object.
Since the only purpose for this is proxying, $state.raw cannot be used in the same way.