[css-containment] reuse "ink overflow" terminology

[frivoal]

This is a follow up form https://lists.w3.org/Archives/Public/www-style/2016Feb/0320.html which was left unresolved.

point 3 of item https://drafts.csswg.org/css-containment/#containment-layout says this:

If the contents of the element overflow the element, they must not project any "geometry" beyond the element’s normal bounds. In particular, any overflow must not be capable of causing the element’s ancestors to overflow; as far as the ancestors are concerned, the element is perfectly confined to its normal width×height bounds.

As far as I can tell, this is trying to define an effect identical to ink overflow, as defined in https://www.w3.org/TR/css-overflow-3/#ink.

Rather than redefining it, we should just reuse that term:

If the contents of the element overflow the element, they must be treated as ink overflow

[frivoal]

@tabatkins: If you're OK with this editorial change, I can go ahead and fix the spec, just give me the green light.

If you think the change would have non editorial consequences, I'd like to hear what these would be, because I don't think there should be any.