Inline nodes in our layout tree have a position, so let's show it. By
centralizing the logic for this, block nodes now lose their redundant
'content-size' dump info which is already part of the box model dump.
This ensures that percentages resolve against the foreignObject's size
instead of the size of its containing block.
This makes user profile pictures clip correctly in the "Friends" view
of the Discord app.
This is according to the default user-agent style from the SVG2 spec.
In order for this to work correctly, we also have to assign width and
height to foreignObject boxes during SVG layout, since they are handled
manually by SVGFormattingContext.
This patch does two things:
1. Makes TreeBuilder never cross the foreignObject boundary when looking
for an appropriate insertion parent. Before this change, we would
sometimes make things inside the foreignObject DOM subtree have
layout nodes outside the foreignObject.
2. Makes foreignObject boxes participate in the anonymous wrapping of
inline-level boxes. This is particularly imporant for absolutely
positioned elements inside foreignObject, which were previously
getting incorrectly wrapped if there was any text (even empty)
preceding the abspos element.
