Clip frames for overflow were applied based on whether the box in
question had a non-identity matrix transformation associated with it.
That however is not correct, since specifying a no-op transform like
`scale(1)` still needs to apply clip overflow rectangles. So instead we
need to check whether the element associated with the box in question
has any CSS transforms.
This appears to have been a regression from
9bbc1cd618 and effectively reverts that
commit, but keeps its effect by unifying on the check for CSS transforms
instead.
This fixes some background boxes being rendered for the invisible items
of the carousels on https://computerbase.de/.
fb9286eccb