feat: simpler hydration of CSS custom property wrappers

[Rich-Harris]

As with #11773, we can simplify CSS custom property wrappers around components — we don't need to wrap the wrapper <div> in hydration comments or do any hydrate_nodes traversal, we can just use the element directly.

We can also put the element in the template, so that we don't need to create it inside the css_props helper. This simplifies the implementation and is less work.

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• 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: bb591c9

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

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[trueadm]

Love it