LibWeb: Add CustomStringConvertible extension for HTMLToken types

Author: https://github.com/ADKaster
Commit: 33e50889f2
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1130
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/dzfrias

Tests/LibWeb/TestHTMLTokenizerSwift.swift

@@ -26,6 +26,8 @@ struct TestHTMLTokenizerSwift {
         default_token.type = .Character(codePoint: "a")
         precondition(default_token.isCharacter())
 
+        print("\(default_token)", to: &standardError)
+
         print("HTMLToken types pass", to: &standardError)
     }