[Feature] expose the metadata from ESBuild bundling?

[vicb]

It would be quite helpful for the OpenNext adapter to have access to the metadata of the ESBuild bundling.
It would allow checking what input files are included and there size (i.e. https://esbuild.github.io/api/#analyze)

We do already generate those metadata during the build but don't dump them to the disk.
I think we could generate an optional <bundle.js>.metafile.json on wrangler deploy --dry-run --outfile

Do you think it's worth it?
If yes, I see 2 options: via an env var (i.e. WRANGLER_GENERATE_METAFILE) or via a --metafile option.

Thoughts?

/cc @petebacondarwin @dario-piotrowicz

related: #7876

[vicb]

@petebacondarwin I re-assigned this to me. My intention was to work on this from the beginning, I only assigned to you as I had questions about how to activate this... but realized it might be confusing :)