fix: correctly backport svelte:element to old AST

[dummdidumm]

Both <svelte:element this="div"> and <svelte:element this={"div"}> were backported as tag: "div" for the old AST. That's wrong because the latter should result in tag: { type: 'Literal', .. }. Fixing this makes all the tests in prettier-plugin-svelte pass with Svelte 5.

Also cleaned up a bit of code in the parser.

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[changeset-bot]

🦋 Changeset detected

Latest commit: e7831e0

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

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