dillon1000/react

Rewrite ReactDOMSelection to use fewer ranges (#9992)

We heard from Chrome engineers that creating too many Range objects slows down Chrome because it needs to keep track of all of them for the case that anchor/focus nodes get removed from the document. We can just implement this calculation without ranges anyway.

jsdom doesn't support Range objects, but I copied the fuzz test code into my browser and manually compared it against our old implementation https://gist.github.com/sophiebits/2e6d571f4f10f33b62ea138a6e9c265c; with 200,000 trials no differences were found.