Router Tree

• This release introduces createRouterTree: a function that is used to build a router tree from an array of routes. Previously, <Router> accepts a plain array of routes however this proved problematic for component preloading and may aggressively regenerate the route tree internally. createRouteTree ensures that the routes are immutable and allows component preloading when performing page/link prefetching.
• <Link> now prefetches lazily with IntersectionObserver.
• <Link> prefetch now defaults to true.