Add mocks for element scrolling methods

Element prototype has several methods to scroll it, but those methods are commented in the sources.

Why did you do this? For example window.scrollTo is a function that does nothing, just prints warning in console. I think that it would be okay for Element.prototype.scroll() method as well.

[M3kH]

How far is this issue to be close?

[thenikso]

I also needed this, I ended up doing something like this:

const el = dom.window.document.querySelector(
    '.myScrollingElement',
  );
el.scrollTop = 12345;
el.dispatchEvent(new dom.window.Event('scroll'));