LibWeb: Implement <desc> SVG element

Author: https://github.com/jamierocks
Commit: 2d90317c20
Pull-request: https://github.com/SerenityOS/serenity/pull/23974
Reviewed-by: https://github.com/MacDue

Userland/Libraries/LibWeb/Forward.h

@@ -637,6 +637,7 @@ class SVGAnimatedRect;
 class SVGCircleElement;
 class SVGClipPathElement;
 class SVGDefsElement;
+class SVGDescElement;
 class SVGElement;
 class SVGEllipseElement;
 class SVGForeignObjectElement;