LibWeb: Implement the <style> SVG element

The `<style>` element is allowed to be in the SVG namespace, so we now
support this element.

It has the same behaviour as the HTML namespace `<style>` element as
described in the spec.

"The semantics and processing of a ‘style’ and its attributes must be
the same as is defined for the HTML ‘style’ element."

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -523,6 +523,7 @@ set(SOURCES
     SVG/SVGRadialGradientElement.cpp
     SVG/SVGSVGElement.cpp
     SVG/SVGStopElement.cpp
+    SVG/SVGStyleElement.cpp
     SVG/SVGSymbolElement.cpp
     SVG/SVGTextContentElement.cpp
     SVG/SVGTitleElement.cpp