Support for ESM in spack

[cmmartin]

My project uses ESM, but spack currently attempts to require('spack.config.js'). I can't use require with module: true, but I also cannot rename the config to spack.config.cjs or it won't be found since it's hardcoded to look for spack.config.js

[muradbu]

Same issue here. The code examples in the docs are shown to use ESM import syntax, so that's a bit contradicting. I'm going to opt with ncc in the meantime.

[lgarron]

I also run into this issue every time I try out swc, which is a few times now. I can't figure out how to use spack in a project with "type": "module", so I always has to dismiss it as a viable option before I can even really try it.

After about a dozen attempts to adapt the demo config file with minimal changes, I'm still stuck with:

> npx spack --config "/Users/lgarron/Code/git/github.com/cubing/cubing.js/spack.config.cjs"
thread '<unnamed>' panicked at 'cannot access a scoped thread local variable without calling `set` first', /Users/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-1.0.1/src/lib.rs:168:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
node:internal/process/promises:289
            triggerUncaughtException(err, true /* fromPromise */);
            ^

[Error: panic detected] { code: 'GenericFailure' }

Node.js v19.7.0

For a lot of web development these days, it is quite feasible to work entirely with ESM code and no CommonJS. It would be really welcoming if that also applied to spack.