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.
We were already always doing this, but through an unusual mechanism:
SVG layout creates a BFC on the stack when laying out foreignObject
subtrees.
This change makes the rest of the layout system aware of this, and
also allows it to be reflected in layout dumps.
Some SVG presentation attributes are only supported on certain
elements. We now support these special cases for attributes and
elements that we currently have implemented.
Browsers such as Chrome and Firefox apply an arbitrary scale to the
current font size if `normal` is used for `line-height`. Firefox uses
1.2 while Chrome uses 1.15. Let's go with the latter for now, it's
relatively easy to change if we ever want to go back on that decision.
This also requires updating the expectations for a lot of layout tests.
The upside of this is that it's a bit easier to compare our layout
results to other browsers', especially Chrome.
