LibWeb: Parse CSS "font-variant" as part of "font"

This allows us to parse CSS "font" values that contain e.g "small-caps"
or "normal", as used on Acid3.

Userland/Libraries/LibWeb/CSS/StyleValue.h

@@ -146,6 +146,11 @@ enum class Float {
     Right,
 };
 
+enum class FontVariant {
+    Normal,
+    SmallCaps,
+};
+
 enum class ImageRendering {
     Auto,
     CrispEdges,