fix: correctly look for sibling elements inside blocks and components

[7nik]

Fixes #15027 and fixes #14995

When the target element is inside a block or component, get_following_sibling_elements was looking only for sibling elements after the block/component. This PR fixes it by starting the search from the begging of the block/component and skipping nodes that go before the target element.

Also, I noticed that selector like .elem:has(+ .not-adjacent-sibling) isn't marked as unused. Example. Though, it's false negative and isn't that bad.

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: 385b6f0

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

[dummdidumm]

thank you!

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@15106