LibWeb: Store computed SVG path data/transforms in LayoutState

This removes the awkward hack to recompute the layout transform at paint
time, and makes it possible for path sizes to be computed during layout.

For example, it's possible to use relative units in SVG shapes (e.g.
<rect>), which can be resolved during layout, but would be hard to
resolve again during painting.

Tests/LibWeb/Ref/reference/simple-svg-mask-ref.html

@@ -1,4 +1,4 @@
-<svg width="200" viewBox="-10 -10 120 120">
+<svg width="120" viewBox="-10 -10 120 120">
   <rect x="-10" y="-10" width="120" height="120" fill="blue" />
   <rect x="50" y="10" width="40" height="80" fill="red"  />
 </svg>