LibWeb: Parse grid display value

Userland/Libraries/LibWeb/CSS/Properties.json

@@ -528,6 +528,7 @@
     "valid-identifiers": [
       "block",
       "flex",
+      "grid",
       "inline",
       "inline-block",
       "inline-flex",

Userland/Libraries/LibWeb/CSS/StyleProperties.cpp

@@ -530,6 +530,8 @@ CSS::Display StyleProperties::display() const
         return CSS::Display::from_short(CSS::Display::Short::Flex);
     case CSS::ValueID::InlineFlex:
         return CSS::Display::from_short(CSS::Display::Short::InlineFlex);
+    case CSS::ValueID::Grid:
+        return CSS::Display::from_short(CSS::Display::Short::Grid);
     default:
         return CSS::Display::from_short(CSS::Display::Short::Block);
     }