add $lib alias to js/tsconfig

[Rich-Harris]

When creating a package with SvelteKit, it's not uncommon to want to import from $lib directly, rather than one of its submodules:

import thing from '$lib';

This works, but it causes red squigglies because the relevant alias doesn't exist in js/tsconfig.json.

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Latest commit: 7d65daf

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

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create-svelte	Patch

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