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.
Use the `writing-mode` property to determine what values should be used
for computing each element's rect on the screen. If it is a vertical
mode, swap the inline and block, lengths and offsets.
This only lays out whole inline formatting contexts vertically, and does
not currently support mixing the two orientations in a single context.
