When searching outside a scroller that contains focus, we should use that scroller's visible box as search origin (not one of its edges).

Actual: Today, when focus F is clipped (being offscreen) inside a scroller A, spatnav uses an edge of A as its search origin when searching outside of it. Using an edge of A when searching outside of A can cause incorrect distance calculations, as we saw in  Issue 891149 .

Expected: Use A's visible box as search origin when searching outside of it. (It's only when searching inside of A that we should start at one of A's edges.)

To summarize:

  (I) Use a "box edge" of A when searching *inside* of a scroller A.
  (II) Use the "visual bounding box" of A when searching *outside* of a scroller A. 

This bug is related to  Issue 891149 .  Issue 891149  corrected the search origin when A itself is focused but not when A contains a clipped and focused element.

We found this problem when discussing https://chromium-review.googlesource.com/c/chromium/src/+/1253523.