There was nothing left in ComputedStyle except the box model metrics,
so this patch gives it a more representative name.
Note that style information is fetched directly from StyleProperties,
which is basically the CSS property name/value pairs that apply to
an element.
This patch makes StyleProperties heap-allocated and ref-counted so that
a LayoutNode can be without one. The ref-counting also allows anonymous
blocks to share style with their parent block.
LayoutText never needs a StyleProperties, since text always inherits
style from its parent element. This is handled by style_properties().
Every LayoutNode indirectly belongs to some Document. For anonymous
LayoutNodes, we simply traverse the parent chain until we find someone
with a Node from which we can get a Document&.
Instead of LibGUI and WindowServer building their own copies of the drawing
and graphics code, let's it in a separate LibDraw library.
This avoids building the code twice, and will encourage better separation
of concerns. :^)
