[fix] Apply class directive after half way transition

[baseballyama]

fix: https://github.com/sveltejs/svelte/issues/7764

Class attributes were reset if outro existed and element had not yet been destroyed. But class directive was not like that. This PR fixed this issue.

Before submitting the PR, please make sure you do the following

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

Tests

• [x] Run the tests with npm test and lint the project with npm run lint

[GauBen]

This was fast! Thank you baseballyama