`onBeforeInput` needs to be monkey patched

Although it is part of the spec the beforeinput event is only available in Chrome at the time of this writing. Neither Firefox nor Safari or IE implement it. But although Chrome has it, it seems to have issues because it can’t be prevented. This breaks the popular slate-react bindings for the slate rich-text-editor component.

We need to normalize the event in compat. There are a few hints on how to do so in the react code base, but they’re somewhat outdated and we need to reassess the current support status in browsers.

[upendradevsingh]

I am not sure if this is the same issue, breaking slate in mobile browser. I am trying to integrate slatejs in my preact application. Everything worked fine on desktop but it broke in the mobile browser (Android - Chrome).

index.es.js:1524 Uncaught (in promise) Error: Cannot resolve a DOM point from Slate point: {"path":[0,0],"offset":7}
    at Object.toDOMPoint (index.es.js:1524)
    at Object.toDOMRange (index.es.js:1538)
    at Object.__ (index.es.js:633)
    at P (hooks.module.js:1)
    at hooks.module.js:1
    at Array.filter (<anonymous>)
    at hooks.module.js:1
    at Array.some (<anonymous>)
    at Object.a.options.__c (hooks.module.js:1)
    at x (preact.module.js:1)

I have created a sample application.

https://github.com/upendradevsingh/slate-demo

[Rafi993]

This can be a browser polyfill independent of preact