Provide lib for modern DOM

This is basically a re-opening of #2910, which @mhegazy asked me to do.

Nowadays TS has the lib compiler option that allow users to selectively choose which core definitions to include or not based on their target.

It would be nice to add a new option similar to dom and dom.iterable for users targetting a modern DOM runtime. Not sure how to name this since W3C has moved from releases to a "living standard" model.

For example, the living standard includes interfaces ChildNode with methods after, before, remove and replaceWith; ParentNode with methods prepend and append.

Those methods have been in Firefox and Chrome for a long while, they're in preview in Edge (17035+).

They are very convenient and there's no reason a dev that targets modern browsers shouldn't be able to do "lib": "dom.living" and use them.

Unfortunately I am not sure if there's a list somewhere of all those new features... except going through the whole standard :(

Beginnen Sie damit, die vollständige Menge der einzubeziehenden modernen DOM-Features zu bestimmen und festzulegen, wie eine neue auswählbare lib neben "dom" und "dom.iterable" benannt werden soll. Die Issue nennt ChildNode- und ParentNode-Methoden als Beispiele, aber es werden keine Dateien oder Tests angegeben. Als abgeschlossen gilt die Aufgabe, wenn Benutzer die neue lib auswählen und die vorgesehenen modernen DOM-Definitionen verwenden können.