fix: render attributes during SSR regardless of case

[Rich-Harris]

This fixes part of #14479 — attributes like viewBox were failing because the name was being lowercased and then used to look up the value, creating a mismatch.

It doesn't fix the client-side error though, which happens because the contents of the <svelte:element> have an HTML template when they need an SVG one. Not yet sure what a good solution to that looks like.

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Playground

pnpm add https://pkg.pr.new/svelte@14492