[WIP] Add svelte-kit adapt package script to create-svelte projects and every example

[babichjacob]

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time: No adapter by default #62 (comment)
• This message body should clearly illustrate what problems it solves. Support questions come up in the Discord server multiple times per day about "broken" app builds, but are solved by just running adapt. This isn't intended to address the separation of build and adapt, but to just make adapt readily available since it is currently necessary to "complete" a build. Feel free to revise or reject this PR if e.x. the commands should be merged instead, making this useless.
• Ideally, include a test that fails without this PR but passes with it. Nothing to test (imo).

Tests

• Run the tests with npm test and lint the project with npm run lint.

[babichjacob]

If this is accepted, I'm not in any hurry to get another release of create-svelte out that includes it, so I shouldn't be doing anything to do with version bumping or changeset or anything along those lines right? Just let it sit until a more desperate update happens that causes this to get published with it as a "bonus"?

On the other hand, if it's needed / wanted for me to do that, I couldn't find the discussion / vent about what things have to be done to get a new version of something ready for publish after about 15 minutes of searching.

[benmccann]

@Conduitry and I had some questions about what the best way to handle this was in #382 and #62 (comment). I personally would lean towards not having two separate commands or having npm run build also run svelte-kit adapt, but might be missing some of the context. @Rich-Harris would you be able to weigh in here?

[babichjacob]

The latest commits switch "adapt" to "postbuild".

I suspect the examples are failing because they run in parallel, so prerendering one is trying to take resources from another. Thinking of ways to fix it / figuring out where to, so I marked this PR as a WIP.

[Rich-Harris]

@Rich-Harris would you be able to weigh in here?

yeah, I've come to the view that svelte-kit build should run adapt if an adapter is specified — it's the least surprising thing. It is useful to have a conceptual separation between building and adapting (since e.g. svelte-kit start runs the production build locally but ignores whatever the adapter did) but the CLI doesn't need to be overly fussy about that separation.

[benmccann]

Addressed by #430