Add ECMAScript 2024 (ES15) summary page and feature support list

[bndkt]

Fixes #7340

Hey @Fyrd, thanks for maintaining this amazing project! I'd like to help with adding the ES15 summary. I'm not sure where to put those summary pages, couldn't find the ES14 one for example in the repo. I added a file based on a really old summary page and would be really glad if you could point me in the right direction.