LibWeb: Add 'object-position' property and 'position' enum

This patch adds the 'object-position' CSS property description to the
json for code generation.
Also the 'position' enum is added. The values of this enum are the
valid inputs to the object-position property from CSS Values-4.

Userland/Libraries/LibWeb/CSS/Enums.json

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

Userland/Libraries/LibWeb/CSS/Properties.json

@@ -1624,6 +1624,18 @@
       "object-fit"
     ]
   },
+  "object-position": {
+    "affects-layout": false,
+    "inherited": false,
+    "initial": "50% 50%",
+    "max-values": 2,
+    "valid-types": [
+      "length [-∞,∞]",
+      "percentage [-∞,∞]",
+      "position"
+    ],
+    "percentages-resolve-to": "length"
+  },
   "opacity": {
     "affects-layout": false,
     "affects-stacking-context": true,