LibWeb: Simplify handling of {text,box}-shadow

We know that shadow values are always parsed as a `KeywordStyleValue`
with `Keyword::None` or a `StyleValueList`

Author: Calme1709

Libraries/LibWeb/CSS/ComputedProperties.cpp

@@ -1381,29 +1381,21 @@ Vector<ShadowData> ComputedProperties::shadow(PropertyID property_id, Layout::No
         };
     };
 
-    if (value.is_value_list()) {
-        auto const& value_list = value.as_value_list();
-
-        Vector<ShadowData> shadow_data;
-        shadow_data.ensure_capacity(value_list.size());
-        for (auto const& layer_value : value_list.values()) {
-            auto maybe_shadow_data = make_shadow_data(layer_value->as_shadow());
-            if (!maybe_shadow_data.has_value())
-                return {};
-            shadow_data.append(maybe_shadow_data.release_value());
-        }
+    if (value.to_keyword() == Keyword::None)
+        return {};
 
-        return shadow_data;
-    }
+    auto const& value_list = value.as_value_list();
 
-    if (value.is_shadow()) {
-        auto maybe_shadow_data = make_shadow_data(value.as_shadow());
+    Vector<ShadowData> shadow_data;
+    shadow_data.ensure_capacity(value_list.size());
+    for (auto const& layer_value : value_list.values()) {
+        auto maybe_shadow_data = make_shadow_data(layer_value->as_shadow());
         if (!maybe_shadow_data.has_value())
             return {};
-        return { maybe_shadow_data.release_value() };
+        shadow_data.append(maybe_shadow_data.release_value());
     }
 
-    return {};
+    return shadow_data;
 }
 
 Vector<ShadowData> ComputedProperties::box_shadow(Layout::Node const& layout_node) const

Libraries/LibWeb/CSS/Interpolation.cpp

@@ -1341,19 +1341,11 @@ RefPtr<StyleValue const> interpolate_box_shadow(DOM::Element& element, Calculati
     //                 (transparent 0 0 0 0) with a corresponding inset keyword as needed to match the longer list if
     //                 the shorter list is otherwise compatible with the longer one
 
-    static constexpr auto process_list = [](StyleValue const& value) {
-        StyleValueVector shadows;
-        if (value.is_value_list()) {
-            for (auto const& element : value.as_value_list().values()) {
-                if (element->is_shadow())
-                    shadows.append(element);
-            }
-        } else if (value.is_shadow()) {
-            shadows.append(value);
-        } else if (!value.is_keyword() || value.as_keyword().keyword() != Keyword::None) {
-            VERIFY_NOT_REACHED();
-        }
-        return shadows;
+    static constexpr auto process_list = [](StyleValue const& value) -> StyleValueVector {
+        if (value.to_keyword() == Keyword::None)
+            return {};
+
+        return value.as_value_list().values();
     };
 
     static constexpr auto extend_list_if_necessary = [](StyleValueVector& values, StyleValueVector const& other) {