LibWeb: Make CSS selector parsing use StyleComponentValueRules

Also added some pseudo-classes that were handled in the deprecated
parser:
- :disabled
- :enabled
- :checked
- :nth-child
- :nth-last-child
- :not

Userland/Libraries/LibWeb/CSS/Parser/StyleFunctionRule.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020-2021, the SerenityOS developers.
+ * Copyright (c) 2021, Sam Atkins <atkinssj@gmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -20,6 +21,17 @@ public:
     StyleFunctionRule();
     ~StyleFunctionRule();
 
+    String const& name() const { return m_name; }
+    Vector<String> const& values() const { return m_values; }
+    // FIXME: This method is a temporary hack while much of the parser still expects a string, rather than tokens.
+    String values_as_string() const
+    {
+        StringBuilder builder;
+        for (auto& value : m_values)
+            builder.append(value);
+        return builder.to_string();
+    }
+
     String to_string() const;
 
 private: