LibWeb: Implement CSS perspective-origin

Author: https://github.com/Psychpsyo
Commit: 2db3796fd3
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6805
Reviewed-by: https://github.com/AtkinsSJ ✅
Reviewed-by: https://github.com/gmta ✅
Reviewed-by: https://github.com/konradekk

Libraries/LibWeb/CSS/ComputedProperties.cpp

@@ -751,6 +751,11 @@ Optional<CSSPixels> ComputedProperties::perspective() const
     VERIFY_NOT_REACHED();
 }
 
+Position ComputedProperties::perspective_origin() const
+{
+    return position_value(PropertyID::PerspectiveOrigin);
+}
+
 TransformOrigin ComputedProperties::transform_origin() const
 {
     auto length_percentage_with_keywords_resolved = [](StyleValue const& value) -> LengthPercentage {