into account only once.
There were two bugs here: (1) relative position applied to
scanned/unscanned text fragments independently of the container element
that applied that relative position, causing double-counting; (2)
relative position applied to inline block fragments independently of the
wrapped block itself, causing double-counting.
This commit also removes the `cascade_anonymous` function and the
related `Fragment` constructor. They were unused, and their
functionality has been replaced by the `modify_style_for_*` series of
functions.
Closes#7067.
