The `package` command does not replace `process.env.*`

Describe the bug

When you run npm run package in a SvelteKit project, process.env references (like process.env.NODE_ENV) are not statically replaced; the files that are output still contain the process.env references.

I don't know if there are cases when this is desirable, but in my case it is not. My library has a few checks for process.env.NODE_ENV === "test" which are only internal. I have a hard time imagining a case when a package user would want anything other than "production" from a third-party library.

In particular, this seems like it causes an issue with Svelte projects built with https://github.com/sveltejs/template where the packaging also does not handle process.env.

Reproduction

It's not a minimal example, but I ran into this with my component library: https://github.com/rgossiaux/svelte-headlessui

You can repro this by checking out & installing the repo, then running npm run package.

A user then reported that the resulting package is broken with https://github.com/sveltejs/template using this example repo: https://github.com/jerriclynsjohn/svelte-headlessui-test-repo

Logs

No response

System Info

System:
    OS: macOS 12.1
    CPU: (10) arm64 Apple M1 Max
    Memory: 7.89 GB / 64.00 GB
    Shell: 3.3.1 - /opt/homebrew/bin/fish
  Binaries:
    Node: 16.8.0 - /var/folders/rn/2kdgb0jj25q2v656j3qc_ywr0000gn/T/fnm_multishells/23841_1640400023703/bin/node
    Yarn: 1.22.17 - /opt/homebrew/bin/yarn
    npm: 7.21.0 - /var/folders/rn/2kdgb0jj25q2v656j3qc_ywr0000gn/T/fnm_multishells/23841_1640400023703/bin/npm
  Browsers:
    Chrome: 97.0.4692.99
    Safari: 15.2

### Severity

serious, but I can work around it

### Additional Information

_No response_

Start by checking out the reproduction repository and running npm run package to inspect the generated files for process.env references. Compare the output with the sveltejs/template consumer example and trace the package build configuration responsible. Done means the packaged library replaces the relevant process.env values and works in the consumer project.