feat: simplify derived object destructuring

[ottomated]

The following $derived

let { foo, bar: [a, b, { baz }]} = $derived(stuff);

currently compiles to

let derived_object = $.derived(() => stuff),
  derived_values = $.derived(() => {
    let { foo, bar: [a, b, { baz }] } = $.get(derived_object);

    return [foo, a, b, baz];
  }),
  foo = $.derived(() => $.get(derived_values)[0]),
  a = $.derived(() => $.get(derived_values)[1]),
  b = $.derived(() => $.get(derived_values)[2]),
  baz = $.derived(() => $.get(derived_values)[3]);

By re-using the extract_paths function, this PR simplifies the output to

let derived_object = $.derived(() => stuff),
  foo = $.derived(() => $.get(derived_object).foo),
  a = $.derived(() => $.get(derived_object).bar[0]),
  b = $.derived(() => $.get(derived_object).bar[1]),
  baz = $.derived(() => $.get(derived_object).bar[2].baz);

which should be more performant because it avoids destructuring twice, and doesn't create as many derived sources.

Also added a test for destructuring an array, which was missing before.

Svelte 5 rewrite

Please note that the Svelte codebase is currently being rewritten for Svelte 5. Changes should target Svelte 5, which lives on the default branch (main).

If your PR concerns Svelte 4 (including updates to svelte.dev.docs), please ensure the base branch is svelte-4 and not main.

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

[changeset-bot]

🦋 Changeset detected

Latest commit: bfb9a4f

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

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[Rich-Harris]

Fantastic! We can actually go a step further, and eliminate the intermediate derived entirely in simple cases:

let foo = $.derived(() => $.get(stuff).foo),
  a = $.derived(() => $.get(stuff).bar[0]),
  b = $.derived(() => $.get(stuff).bar[1]),
  baz = $.derived(() => $.get(stuff).bar[2].baz);