Migrate classic buildpack to artifact inventory code

[mlarraz]

The changes in #814 intentionally skipped these files used exclusively by the classic buildpack:

• https://github.com/heroku/buildpacks-nodejs/blob/main/common/nodejs-utils/src/bin/generate_inventory.rs
• https://github.com/heroku/buildpacks-nodejs/blob/main/common/nodejs-utils/src/bin/resolve_version.rs

Migrating these is a blocker to allowing the classic buildpack to support ARM64: heroku/heroku-buildpack-nodejs#1268

The generate_inventory script appears to have been superseded by the update_node_inventory, but this does not work on the classic buildpack because it expects the Changelog entries to follow strict semver, which it does not.