Inline formatting contexts in vertical writing modes were measuring
intrinsic width from the line box width. That width still tracks the
line-height-sized horizontal span, so shrink-to-fit abspos sizing could
stay at 50px even when the text fragments only covered 25px.
Measure the physical horizontal extent from the line box fragments
instead, including the float-aware block formatting context path. This
makes orthogonal inline content report the correct intrinsic width.
