esm: unflag --experimental-exports

This removes the experimental --experimental-exports flag to make the support on by default.

This PR should not land until we have:

• Resolution on package-relative loading PR (https://github.com/nodejs/node/pull/29327)
• Consensus to land from the modules group

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines