chore(auth): Convert @redwoodjs/auth to ESM+CJS dual build

[Tobbe]

With this PR we now dual-build the @redwoodjs/auth package to output both CJS and ESM.

@redwoodjs/auth is used by @redwoodjs/web, all the auth providers, @redwoodjs/testing and a few more. It could also be used directly by users' apps if, for example, they implement a custom auth provider. So for now we need to provide both ESM and CJS builds of the package.

The most tricky thing here was to get the .js/.cjs/.mjs stuff right. I tried explaining it in comments in build.ts
arethetypeswrong is super helpful
Also see this issue for more info evanw/esbuild#2600

Another valuable discovery here was that isolateModules is required for esbuild. https://esbuild.github.io/content-types/#isolated-modules

[jtoar]

Looking good so far, caught two small things. Types are looking good as well:

$ yarn dlx @arethetypeswrong/cli ./redwoodjs-auth.tgz

@redwoodjs/auth v7.0.0

Build tools:
- typescript@5.4.3

👺 Import resolved to an ESM type declaration file, but a CommonJS JavaScript file. https://github.com/arethetypeswrong/arethetypeswrong.github.io/blob/main/docs/problems/FalseESM.md


┌───────────────────┬────────────────────────┐
│                   │ "@redwoodjs/auth"      │
├───────────────────┼────────────────────────┤
│ node10            │ 🟢                     │
├───────────────────┼────────────────────────┤
│ node16 (from CJS) │ 👺 Masquerading as ESM │
├───────────────────┼────────────────────────┤
│ node16 (from ESM) │ 🟢 (ESM)               │
├───────────────────┼────────────────────────┤
│ bundler           │ 🟢                     │
└───────────────────┴────────────────────────┘

Some others I'm noticing as I'm reviewing

• still some files with an .mts extension that could just be a .ts extension (the vite config files namely)