Add __meta property to BCD build

[queengooborg]

This PR fixes #7358 by adding a __meta property to the BCD root, containing the build's version number. This allows for easier access of the version number for NodeJS users, and straight-up allows access for Deno/browser/Python/etc. users entirely.

[foolip]

This change is not without risk and I think would require at least a minor version bump. I am fairly skeptical of making this change unless there are multiple requests from BCD consumers.

[queengooborg]

I think that we should include this in a major semver bump actually, since it is a potentially breaking change. In doing so, however, this might help our consumers understand that keys starting with __ are special in BCD, such as compatibility info or otherwise.

I think if we are to do this, we should land it around the same time we start releasing ESM builds.

[caugner]

LGTM, but ...

1. ... wouldn't it make sense to wrap the version in a __meta object (with one key version), so that we can extend this in the future?
2. ... this is probably a breaking change for consumers that just loop over the data (and this makes me wonder if we have other breaking changes in the pipeline - possibly among your open PRs - that should be bundled with this).

[github-actions]

This pull request has merge conflicts that must be resolved before we can merge this.

[caugner]

LGTM

[github-actions]

This pull request has merge conflicts that must be resolved before we can merge this.

[queengooborg]

I'm going to hold off on merging this for the time being since it is a major semver bump. I'd like to get other changes merged alongside this one before the next release.

[caugner]

@queengooborg Would it make sense to create a v5 branch for this?

[queengooborg]

Maybe so, yeah -- my plan was originally to hold off on a v5 release until #16232 is merged (and maybe the ESM internal upgrades), but also to hold off so we get a v4.2.0 release... :D