Prefer proposal-composites to proposal-richer-keys

[CxRes]

It seems proposal-richer-keys has been unmaintained for many years, whereas proposal-composites is being actively developed. The latter has a polyfill with tests, which you could bring over quite easily. Would you please consider switching?

[zloirock]

Thanks for the issue. Of course, I'm following the progress of these proposals. If it's not an obvious feature, lately, I've been preferring to add polyfills for proposals that have reached at least stage 2 or 2.7, as they too often have major changes before that. The problem with this proposal is that it also requires patching of collection constructors and methods that will cause a significant slowdown when any of the collections usage. So I'd prefer to add a polyfill for this proposal on stage 2.7 or even 3.