doc: document considerations for inclusion in core

[Trott]

Document the things that are considered when making the determination as
to whether something should or shouldn't be in core. This does not (yet,
at least) attempt to address how to include modules in core. (Should
it be in the Node.js code base or vendored in from a separate
repository?) It is limited to whether something should be in core or
not.

Closes: nodejs/TSC#1041

[Trott]

@nodejs/tsc This is very much a first draft, but also possibly fit to land and be iterated upon to add more information. This is mostly a summary of what @mhdawson, @jasnell, and @ronag stated in https://github.com/nodejs/node/discussions/39779. There are other things that could be included in this document, but I don't think it pays to be exhaustive. I think we just want to include the most important elements and try to keep things to a length that people are likely to read and retain.

[Trott]

One thing I didn't include in the document, but perhaps I should: Once something is in core, it becomes all but impossible to remove it. "No" is "not now" but "yes" is forever.

[Trott]

I think this is ready for some more reviews.

I'd like to stress that what I'm hoping for is to reach consensus that having this document as it stands is better than not having this document. If we try to get consensus that this is exactly right before landing, it will probably never land. We can always iterate on it after it lands.

[mhdawson]

LGTM

[mhdawson]

I'll probably submit a follow on PR to tweak a bit as it may still be a bit module/package specific but I think that its fine to do that in a follow on PR versus bikeshedding in this one :)

[github-actions]

Landed in 5c7af3f...89c0577