fix: create <svelte:element> instances with the correct namespace

[Rich-Harris]

#9645 WIP. I think the best thing to do here is keep a reference to the current parent node in the transform state, but I'm not quite sure where to put that, and right now I'm hunched over a laptop on a cramped train which makes it difficult to navigate the codebase effectively to figure it out

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[dummdidumm]

Closing in favor of #10006