[dom] classList.toggle(clsName, boolValue) (#160)

I find it useful if we had something like `element.classList.toggle('active', someBoolean)` that would do add the class if the boolean is true, and remove it otherwise. without the second argument it would be the current `.toggle(clsName)` function, where the boolean is `element.classList.contains(clsName)` actually


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https://github.com/whatwg/dom/issues/160