Fixes#41258
When we detect `type: "module"` in `package.json`:
~1. generate `server.mjs`~ Not necessary when `type: "module"` is set.
2. use `import` instead of `require`
3. replace `__dirname` with [ESM compatible
alternative](https://blog.logrocket.com/alternatives-dirname-node-js-es-modules/)
In this PR, I also moved some tests (those using `output: "standalone"`)
to a new `test/production/standalone-mode` directory for easier
discoverability in the future.
Run the related test with `pnpm test
test/production/standalone-mode/type-module/index.test.ts`
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
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