LibWeb: Parse the CSS position type automatically

This means `object-position` will no longer incorrectly accept the
3-value background-position syntax.

Remove the now-ambiguous and unused `position` enum while we're at it.
(This enum only existed as a hack.)

Userland/Libraries/LibWeb/CSS/Enums.json

@@ -319,13 +319,6 @@
     "all",
     "none"
   ],
-  "position": [
-    "left",
-    "right",
-    "top",
-    "bottom",
-    "center"
-  ],
   "positioning": [
     "absolute",
     "fixed",

Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -5930,12 +5930,6 @@ Parser::ParseErrorOr<NonnullRefPtr<StyleValue>> Parser::parse_css_value(Property
         if (auto parsed_value = parse_math_depth_value(component_values))
             return parsed_value.release_nonnull();
         return ParseError::SyntaxError;
-    case PropertyID::ObjectPosition:
-        // FIXME: This should use a parse_position compatible to VALUES-4
-        //        and not the background position, which is almost the same.
-        if (auto parsed_value = parse_comma_separated_value_list(component_values, [this](auto& tokens) { return parse_single_background_position_value(tokens); }))
-            return parsed_value.release_nonnull();
-        return ParseError::SyntaxError;
     case PropertyID::Overflow:
         if (auto parsed_value = parse_overflow_value(component_values))
             return parsed_value.release_nonnull();
@@ -6130,6 +6124,11 @@ Optional<Parser::PropertyAndValue> Parser::parse_css_value_for_properties(Readon
         }
     }
 
+    if (auto property = any_property_accepts_type(property_ids, ValueType::Position); property.has_value()) {
+        if (auto maybe_position = parse_position_value(tokens))
+            return PropertyAndValue { *property, maybe_position };
+    }
+
     if (auto property = any_property_accepts_type(property_ids, ValueType::Ratio); property.has_value()) {
         if (auto maybe_ratio = parse_ratio_value(tokens))
             return PropertyAndValue { *property, maybe_ratio };

Userland/Libraries/LibWeb/CSS/Properties.json

@@ -1628,13 +1628,9 @@
     "affects-layout": false,
     "inherited": false,
     "initial": "50% 50%",
-    "max-values": 2,
     "valid-types": [
-      "length [-∞,∞]",
-      "percentage [-∞,∞]",
       "position"
-    ],
-    "percentages-resolve-to": "length"
+    ]
   },
   "opacity": {
     "affects-layout": false,