chore: finish up const tag work

[Rich-Harris]

small follow-up to #11908. In the process of making a small simplification (removing const_tags, and just using the declaration map) I found another latent bug in our scope handling, relating to elements in SSR. this fixes it

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[dummdidumm]

Yeah there may be more of those kinds of "not the right scope" things happening which happen to not fail because of how the code is written / we don't use scope in that situation. #11798 was another of those