BindingsGenerator: Use `get_attribute_value` for reflected strings

Per:

https://dom.spec.whatwg.org/#concept-reflect

We should be calling `get_attribute_value` for reflected IDL strings.
No functional change as nowhere is performing a reflect on a nullable
type, and just ends up simplifying the code.

Meta/Lagom/Tools/CodeGenerators/LibWeb/BindingsGenerator/IDLGenerators.cpp

@@ -2445,16 +2445,9 @@ static void collect_attribute_values_of_an_inheritance_stack(SourceGenerator& fu
 
             if (attribute.extended_attributes.contains("Reflect")) {
                 if (attribute.type->name() != "boolean") {
-                    // FIXME: This should be calling Element::get_attribute_value: https://dom.spec.whatwg.org/#concept-element-attributes-get-value
-                    if (attribute.type->is_nullable()) {
-                        attribute_generator.append(R"~~~(
-    auto @attribute.return_value_name@ = impl->attribute(HTML::AttributeNames::@attribute.reflect_name@);
-)~~~");
-                    } else {
-                        attribute_generator.append(R"~~~(
-    auto @attribute.return_value_name@ = impl->attribute(HTML::AttributeNames::@attribute.reflect_name@).value_or(String {});
+                    attribute_generator.append(R"~~~(
+    auto @attribute.return_value_name@ = impl->get_attribute_value(HTML::AttributeNames::@attribute.reflect_name@);
 )~~~");
-                    }
                 } else {
                     attribute_generator.append(R"~~~(
     auto @attribute.return_value_name@ = impl->has_attribute(HTML::AttributeNames::@attribute.reflect_name@);
@@ -3044,16 +3037,9 @@ JS_DEFINE_NATIVE_FUNCTION(@class_name@::@attribute.getter_callback@)
                     // FIXME: 7. If contentAttributeValue corresponds to a state of attributeDefinition with no associated keyword value, then return null.
                 }
             } else if (attribute.type->name() != "boolean") {
-                // FIXME: This should be calling Element::get_attribute_value: https://dom.spec.whatwg.org/#concept-element-attributes-get-value
-                if (attribute.type->is_nullable()) {
-                    attribute_generator.append(R"~~~(
-    auto retval = impl->attribute(HTML::AttributeNames::@attribute.reflect_name@);
-)~~~");
-                } else {
-                    attribute_generator.append(R"~~~(
-    auto retval = impl->attribute(HTML::AttributeNames::@attribute.reflect_name@).value_or(String {});
+                attribute_generator.append(R"~~~(
+    auto retval = impl->get_attribute_value(HTML::AttributeNames::@attribute.reflect_name@);
 )~~~");
-                }
             } else {
                 attribute_generator.append(R"~~~(
     auto retval = impl->has_attribute(HTML::AttributeNames::@attribute.reflect_name@);