[css-scroll-anchoring-1] Anchor node selection algorithm should specify how inline elements are traversed

[eqrion]

The anchor node selection section specifies that:

The anchor node is either a non-anonymous block box or a text node.

Then later there is an candidate examination algorithm given for calculating the anchor node. This algorithm doesn't make any mention of how to handle inline elements, so it's not clear how we're supposed to guarantee that the anchor node is only a non-anonymous block box or text node.

Blink will descend into them to find an anchor node, and then continue if one is not found. This is the sane thing to do, and how we've implemented it in Gecko, but it should be made more explicit in the algorithm.

[eqrion]

cc @dbaron @theres-waldo @skobes