refactor: only run webpack once for multi-arch packages

[MarshallOfSound]

Fixes #3436

This is a follow up to #3433 that optimizes the build to only run webpack once and instead generate a hash<->path mapping between native modules and their respective paths on disk.

This handles:

• Multiple native modules having the same hash
• Modules not being mappable

This might fall apart:

• If the same native module built for different arches ends up in a different place on disk (this probably isn't compatible with webpack anyway, so probs all good here)

Example: