Svelte: Support 5.0.0-next.65 prerelease

[JReinhold]

What I did

1. Updated the renderToCanvas logic to use the new mounting API (documented here, introduced in breaking: remove createRoot, adjust mount/hydrate APIs, introduce unmount sveltejs/svelte#10516
2. Refactored the Svelte 4+5 support, splitting it up to make it more maintainable in the future.
3. General refactor of a few Svelte exports and components.

Hopefully this should be all that's needed to support basic rendering in Svelte 5, but given it's still in prerelease mode they can release breaking changes at any moment, so we can't really guarantee support beyond the exact prerelease version I've tested against.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This pull request has been released as version 0.0.0-pr-26188-sha-982be2de. Try it out in a new sandbox by running npx storybook@0.0.0-pr-26188-sha-982be2de sandbox or in an existing project with npx storybook@0.0.0-pr-26188-sha-982be2de upgrade.

More information

Published version	0.0.0-pr-26188-sha-982be2de
Triggered by	@JReinhold
Repository	storybookjs/storybook
Branch	jeppe/svelte-5-prerelease
Commit	982be2de
Datetime	Mon Feb 26 15:21:18 UTC 2024 (1708960878)
Workflow run	8051277593

To request a new release of this pull request, mention the @storybookjs/core team.

core team members can create a new canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=26188

[JReinhold]

Self-merging, @kasperpeulen to review later.