fix: migrate derivations without semicolons

[paoloricciuti]

Svelte 5 rewrite

Closes #11689 ...i've tried to think of a "general" solution that didn't involve the if but i wasn't able to figure out one because only appending would not work for cases where there's a parentheses and a semicolon since those are "ignored" by the ast and only updating doesn't work when there's no semicolon and no parentheses since then end of the expression and end of the node are the same.

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[dummdidumm]

Thank you!