add navigation (but not invalidation) types

[Rich-Harris]

A more conservative version of #6522.

There's some controversy about whether invalidate(...) and invalidateAll() should trigger beforeNavigate and afterNavigate callbacks and update the navigating store. There are good arguments on both sides.

I think it makes sense to merge the changes without the invalidation stuff in the meantime, since it's a non-breaking change that will add a useful feature and close an issue.

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