Fix check for left/right annotations

We're only interested in annotations immediately to the left/right
so just take those and see if they are content offsets, instead
of using getNearestContentOffset, which breaks if you place it
inside a handlesOwnChildrenNode.

Bug: 68588
Bug: 68597
Change-Id: Ib791e5988078496411aa974afa0a90ebce10e737