Phase out screenreader-trap and keyboard-trap in favor of inert polyfill?

[ianmcburnie]

The inert attribute is now available in modern browsers. It's probably time to start thinking about making the switch to using it (and a polyfill) instead of keyboard-trap and screenreader-trap

Inert attribute: https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/inert

Polyfill: https://github.com/WICG/inert