inert to be supported by all browsers

[salbeira]

Right now we use a polyfill to make inertness work on invisible or inactive elements but according to caniuse the inert attribute will be supported by all browsers. In particular firefox will have support in version 112. Right now I have 111 installed and my system tells me I am up to date, so I expect it to become available to the common user very soon.

When should we remove the polyfill from our dependencies?

[mbotsch]

Let's remove the polyfill now