[breaking] prerender shells when ssr false and prerender not false

[dummdidumm]

Closes #3966

This is a breaking change insofar that pages that have export const ssr = false and not explicitly set export const prerender = false or prerender.entries: [] will have their handle hooks run, which could be unexpected and cause unintended side effects. In that's the case for you, add export const prerender = false next to wherever you have export const ssr = false.

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[dummdidumm]

duplicated to code a little further below, but this way it's more readable (you don't need to hold all these conditions in your head until you arrive at the other condition)

[dummdidumm]

Ha, this uncovered an unrelated bug in write_types. I removed the check for now to get CI green. When I open the PR to fix it I'll reenable it.