fix: disallow $state/$derived in const tags

[Rich-Harris]

alternative to #15044. closes #15042

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Playground

pnpm add https://pkg.pr.new/svelte@15115

[paoloricciuti]

This doesn't cover the $state or $props case right?

I think we should just special case $state.snapshot in #15044

[Rich-Harris]

$props() is already accounted for, and state is handled with the same logic as derived

[paoloricciuti]

$props() is already accounted for, and state is handled with the same logic as derived

Oh gotcha...well I guess is better then...close mine