LibWeb: Hide stepper buttons on appearance: textfield number inputs

The spec says:

> For the purpose of this specification, they all have the same effect
  as auto. However, the host language may also take these values into
  account when defining the native appearance of the element.

https://drafts.csswg.org/css-ui/#typedef-appearance-compat-special

Firefox at least hides the stepper buttons when this is set.

Libraries/LibWeb/CSS/ComputedProperties.cpp

@@ -833,8 +833,6 @@ Appearance ComputedProperties::appearance() const
     auto appearance = keyword_to_appearance(value.to_keyword()).release_value();
     switch (appearance) {
     // Note: All these compatibility values can be treated as 'auto'
-    case Appearance::Textfield:
-    case Appearance::MenulistButton:
     case Appearance::Searchfield:
     case Appearance::Textarea:
     case Appearance::PushButton:
@@ -849,6 +847,10 @@ Appearance ComputedProperties::appearance() const
     case Appearance::Button:
         appearance = Appearance::Auto;
         break;
+    // NB: <compat-special> values behave like auto but can also have an effect. Preserve them.
+    case Appearance::Textfield:
+    case Appearance::MenulistButton:
+        break;
     default:
         break;
     }