We erroneously treat {@html ...} tags as a block effect, when really it's more like a template effect. The distinction isn't hugely important today, but it will become more significant with some future work that's planned, so merging this will reduce the size of an upcoming diff.

It also means we only need to create one effect per {@html ...} tag instead of two.

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