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/StyleBlockRule.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
  */
@@ -18,6 +19,12 @@ public:
     StyleBlockRule();
     ~StyleBlockRule();
 
+    bool is_curly() const { return m_token.is_open_curly(); }
+    bool is_paren() const { return m_token.is_open_paren(); }
+    bool is_square() const { return m_token.is_open_square(); }
+
+    Vector<String> const& values() const { return m_values; }
+
     String to_string() const;
 
 private: