LibWeb: Layout SVG <text> elements during layout (not while painting)

Previously, all SVG <text> elements were zero-sized boxes, that were
only actually positioned and sized during painting. This led to a number
of problems, the most visible of which being that text could not be
scaled based on the viewBox.

Which this patch, <text> elements get a correctly sized layout box,
that can be hit-tested and respects the SVG viewBox.

To share code with SVGGeometryElement's the PathData (from the prior
commit) has been split into a computed path and computed transforms.
The computed path is specific to geometry elements, but the computed
transforms are shared between all SVG graphics elements.

Userland/Libraries/LibWeb/SVG/SVGTextContentElement.h

@@ -21,6 +21,8 @@ public:
 
     Optional<TextAnchor> text_anchor() const;
 
+    DeprecatedString text_contents() const;
+
 protected:
     SVGTextContentElement(DOM::Document&, DOM::QualifiedName);