LibWeb: Add list-style-type: disclosure-{closed,open}

These markers are rendered as equilateral triangles pointing right and
down respectively. As we currently don't implement writing-mode the
closed marker does not respect it.

Userland/Libraries/LibWeb/CSS/Enums.json

@@ -179,6 +179,8 @@
         "decimal",
         "decimal-leading-zero",
         "disc",
+        "disclosure-closed",
+        "disclosure-open",
         "lower-alpha",
         "lower-latin",
         "lower-roman",

Userland/Libraries/LibWeb/CSS/Identifiers.json

@@ -108,6 +108,8 @@
   "decimal-leading-zero",
   "default",
   "disc",
+  "disclosure-closed",
+  "disclosure-open",
   "distribute",
   "dotted",
   "double",