per #16255 (comment), this scratches an itch I've had for a while: we put a lot of stuff on context.state.analysis that doesn't really form part of the analysis phase, it's just a convenient place to stick it.

It would be more convenient if that stuff was part of the global state exported from state.js — just as we guard dev-only compiler logic in if (dev) rather than if (context.state.analysis.dev) we could also do if (runes), for example.

While doing this I realised that we don't need to do state.reset inside parse(...), because we only actually need to reset source and locator. This means parse no longer needs to take an unused filename option, so we can remove this in Svelte 6 and make that API simpler.

This PR doesn't replace all the occurrences of context.state.analysis.runes (and .name, etc) because that would likely create merge conflicts. That can be done as an easy follow-up when there's less stuff in the PR queue.

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