[cssom-view] Add a none value to the ScrollBehavior

[jihyerish]

In the CSSOM, there is a ScrollIntoViewOptions and it takes ScrollBehavior and ScrollLogicalPosition.

I think ScrollBehavior needs to have "none" to specify not to scroll an element.
The "none" value could help developer prevent unintentional scrolling.

In fact, there is a discussion whatwg/html#2787 about adding scrollOptions for Element.focus().
The suggested scrollOptions has "none" value for specifying not to scroll the element. Instead of defining new scrolling behavior, it seems reasonable to reference ScrollBehavior in here. So how about adding "none" value to it?

[jihyerish]

In whatwg/html#2787, it was agreed not to add "none" to ScrollBehavior.
Instead of that, there is a suggestion about newly defining "FocusOptions" dictionary with 'preventScroll' boolean option.
So I think this issue would be closed.