System/Libraries/(Css,Graphics2D,Html): Support underlined text

This commit adds the necessary functions to minimally implement support
for CSS text-decoration: underline.

System/Libraries/Html/Tokenizer.HC

@@ -97,6 +97,7 @@ class @html_dom_node : JsonElement
     U8* fontFamily;
     I64 fontSize;
     I64 fontWeight;
+    I64 textDecoration;
     Bool italic;
     Bool display_block;
 };