[css-gaps-1] Allow row decoration breaks in Multicol (with column-wrap)

[jav099]

Somewhat separately from the ongoing segments vs intersections discussion, we still have an open question about whether multicol row gaps should allow row decorations to break, similar to the behavior in grid containers.

From the discussion linked above, it seems clear that the default behavior we want is for the row decoration to run continuously across the multicol container, without breaking:

However, it still might make sense for authors should have the option to intentionally break this decoration, mirroring what grid (or flex) containers could allow, resulting in something like this:

One concern, raised by @rachelandrew, is that broken row decorations in multicol layouts may complicate or confuse the reading order, but perhaps the fact that the default behavior would be for the row decoration to run continuously across the multicol container is enough to alleviate this.
Nevertheless, if this is generally considered to be very detrimental to readability, then perhaps we should not allow breaks at all.

So essentially, should we or should we not give authors the option? So far, we tend to lean towards giving authors the option, since this would make the behavior somewhat consistent across display types.

Thanks!