types: Restricts `preact.config.js`'s `env` types to a more idiomatic subset

[rschristian]

What kind of change does this PR introduce?

refactor of preact.config.js types

Did you add tests for your changes?

N/A

Summary

Goes along with #1734

env in preact.config.js is quite overloaded and has numerous semi-duplicated values: production and isProd, ssr and isServer, etc. I'd like to cut this down to just isProd, isDev, and isServer in v4, but for now, a good start would be to restrict the types & update the wiki.

At best, the types/values beyond these three (and their duplicates) are just convenience (not having to get the path for src yourself), and at worst, confuse new users.

Does this PR introduce a breaking change?

No

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 3efc14d4f0878a6978d1f30485692f3169c8d19b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
preact-cli	Patch

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[developit]

Is isServer the one for prerendering? I regret calling it "SSR" here haha

[rschristian]

Yes, isServer is the one for prerendering.

Regret it as in think it should change to something else? isPrerender?

[developit]

Yeah, SSR is a bit of a misnomer there. Unless folks are still abusing it for SSR? haha

[rschristian]

Some still are or at least want to, but I've been dissuading.

I'm somewhat partial to isServer as it doesn't really mean 'Server' as in 'SSR' (even if that's what it's used for) but the server Webpack config. We have webpack-server-config.js in the source and so it makes sense that you'd use isServer to peek inside/edit that config.

That might just be me doing mental gymnastics to justify what I'm familiar with though.