Add setting hidden attribute back to hide action

[aghassemi]

#7785 added setting hidden attribute to elements that get hidden by calling the hide action or component.collapse() but #7879 removed it because the change broke some components such as lightbox.

The reason for breakage was that some components assumed collapse() only sets display:none and had code that would only reset display to show.

We should bring back setting hidden attribute to hide action because it is semantic. Solution might be as simple as moving the logic to our toggle helper function (not the toggle action) but requires some manual testing to be sure it won't have side-effects.

[aghassemi]

This has been handled already: https://github.com/ampproject/amphtml/blob/master/src/style.js#L230