[css-scroll-anchoring-1] Anchor selection can pick node inside of descendant scrolling element

[eqrion]

The anchor selection algorithm for a scrolling element can select a node that's inside of a descendant scrolling element.

Is there a special case this is needed for?

It seems like the anchor node moving would cause duplicate scroll adjustments to the scrolling element and descendant scrolling element.

[eqrion]

cc @dbaron @theres-waldo @skobes