fix: correctly infer <a> tag namespace

[dummdidumm]

<a> tags are valid in both the SVG and HTML namespace. If there's no parent, we therefore have to look downwards to see if it's the parent of a SVG or HTML element.

fixes #7807
fixes #13793

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[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14134-svelte.vercel.app/

this is an automated message

[pkg-pr-new]

pnpm add https://pkg.pr.new/svelte@14134

commit: 7e70188

[trueadm]

Whilst this is better, it still doesn't feel perfect. Ultimately, I think we need to determine this somehow at runtime but let's get this improvement in first.