Attr.cloneNode() should return Attr, not Node

[fonsp]

Expectation

Attr extends Node, but Attr.cloneNode() returns a new Attr, not just a Node.

Chrome dev tools:

Reality

But in lib.dom.d.ts, its return type is Node. This can give false errors, like this example from the VS Code TS linter:

[IllusionMH]

It's just special case of microsoft/TypeScript#283
#811 was reverted as it broke libs in DefinitelyTyped