breaking: Standardize resolution order for exported options from route files

[elliott-with-the-longest-name-on-github]

This PR (somewhat by accident) accomplishes two goals:

• It parallelizes (or... concurrentizes? 🤷🏻) analyse, resolving all Promise-creating functions together. This should hypothetically speed it up for systems that have the resources to make use of the concurrency; previously we were await-ing inside the loops.
• And, the reason I started this: It fixes the resolution order for config, prerender, and entries -- they were inconsistent.

The correct resolution order for route-file exports is: +page, +page.server, +server, +layout, +layout.server. The old resolutions were... pretty much all different:

• prerender: +page, +page.server, +layout, +layout.server, (false, if a page existed, even if +server exported prerender), +server
• config: Honestly bonkers: Merged shallowly down the layout-page tree, except that each layer would only respect universal ?? server, all of which would hard-override anything exported from +server.
• entries: Less-insane, but still wrong: +server, +page, +page.server (entries not applicable to layouts)

These have all been standardized, and are also way easier to reason about than in their current format:

	return {
		methods: [...new Set([...endpoint.methods, ...page.methods])],
		prerender: page.prerender ?? endpoint.prerender ?? layout.prerender,
		entries: page.entries ?? endpoint.entries, // layouts can't have entries
		config: {
			...layout.config,
			...endpoint.config,
			...page.config
		}
	};

config is also merged more sensically now:

		current = {
			...current,
			...(node?.server?.config ?? {}),
			...(node?.universal?.config ?? {})
		};

Previously, only server OR universal would get merged into the final config at each level.

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[Rich-Harris]

too late 👀

[elliott-with-the-longest-name-on-github]

too late 👀

The test was whether you could follow directions, you failed

[Rich-Harris]

I think this is one of those cases where it really doesn't make sense to worry about parallelizing promise resolution. No actual work is happening beyond importing modules, so the gains are likely non-existent (and quite possibly offset by all the extra async/await stuff we need to do as a result). I'm going to change it so that we just await everything at the top, which should make the code a bit simpler

[Rich-Harris]

Ok thinking out loud a bit more:

• prerender — if there's a +page and a +server, then +server should be disregarded altogether (in fact it should be an error if this route is prerenderable, I'm not sure why it isn't already). So page.prerender ?? endpoint.prerender ?? layout.prerender isn't quite right
• we shouldn't be mixing and matching +server config with +layout config. They're supposed to be independent; layouts are a page concept. (This isn't very clear in the docs.) I feel like it should probably be an error if you have an endpoint and a page together, and the endpoint config disagrees with the (layout+page) config

[Rich-Harris]

have put up an alternative PR #11256

[Rich-Harris]

merged #11256, so I'll close this